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• Multiband quadrupole topological photonic crystals. • Quadrupole moments quantized by glide symmetries. • Multiple Fano resonance immune to structural imperfection. • Quadrupole moment-induced topological edge and corner states. • Coherent coupling of topological edge and corner states. Disorder-immune corner states in quadrupole topological photonic crystals (QTPCs) have recently attracted great attention in the community of photonics. Up to date, however, quadrupole topological systems have been investigated only in single bandgap, while multiband quadrupole ones are preferable for practical applications. In this work, we, for the first time, propose multiband QTPCs with glide symmetries. Due to the intrinsic structural symmetry, all photonic bandgaps have vanishing dipole moments and the majority of them have nontrivial quadrupole moments quantized to integer multiples of 1/4. The QTPCs have, therefore, multiple open quadrupole bandgaps for proper structural parameters, bringing forth multiband topological edge and corner states at their interfaces. In topological edge waveguide coupled with a cavity supporting corner states, the coherent coupling of topological edge and corner states results in multiple Fano resonances with high Q-factors in the order of 104. Their performances are immune to structural disorder or defects, since all photonic modes used for observing the Fano resonances are topologically protected. The presented results have fundamental importance and will find wide photonic applications such as multi-wavelength biosensing and efficient nonlinear frequency conversion. [ABSTRACT FROM AUTHOR]

We report a cryogenic transimpedance amplifier (TA) suitable for cross-correlation current-noise measurements. The TA comprises homemade high-electron-mobility transistors with high transconductance and low noise characteristics, fabricated in an AlGaAs/GaAs heterostructure. The low input-referred noise and wide frequency band of the TA lead to a high resolution in current-noise measurements. The TA's low input impedance suppresses unwanted crosstalk between two distinct currents from a sample, justifying the advantage of the TA for cross-correlation measurements. We demonstrate the high resolution of a TA-based experimental setup by measuring the shot noise generated at a quantum point contact in a quantum Hall system. [ABSTRACT FROM AUTHOR]

The quantum statistical fluctuations of electromagnetic fields establish a limit, known as the shot-noise limit, on the sensitivity of optical measurements performed with classical technologies. However, quantum technologies are not constrained by this shot-noise limit. In this regard, the possibility of using every photon produced by quantum sources of light to estimate small physical parameters, beyond the shot-noise limit, constitutes one of the main goals of quantum optics. Here, we experimentally demonstrate a scalable protocol for quantum-enhanced optical phase estimation across a broad range of phases, with neither pre- nor post-selected measurements. This is achieved through the efficient design of a source of spontaneous parametric downconversion in combination with photon-number-resolving detection. The robustness of two-mode squeezed vacuum states against loss allows us to outperform schemes based on N00N states, in which the loss of a single photon is enough to remove all phase information from a quantum state. In contrast to other schemes that rely on N00N states or conditional measurements, the sensitivity of our technique could be improved through the generation and detection of high-order photon pairs. This unique feature of our protocol makes it scalable. Our work is important for quantum technologies that rely on multiphoton interference such as quantum imaging, boson sampling, and quantum networks. [ABSTRACT FROM AUTHOR]

We present a three-party reference frame independent quantum key distribution protocol which can be implemented without any alignment of reference frames between the sender and the receiver. The protocol exploits entangled states to establish a secret key among three communicating parties. We derive the asymptotic key rate for the proposed protocol against collective attacks and perform a finite-size key security analysis against general attacks in the presence of statistical fluctuations. We investigate the impact of reference frame misalignment on the stability of our protocol, and we obtain a transmission distance of 180 km, 200 km, and 230 km for rotation of reference frames β = π /6, β = π /8 and β = 0, respectively. Remarkably, our results demonstrate that our proposed protocol is not heavily affected by an increase in misalignment of reference frames as the achievable transmission distances are still comparable to the case where there is no misalignment in reference frames (when β = 0). We also simulate the performance of our protocol for a fixed number of signals. Our results demonstrate that the protocol can achieve an effective key generation rate over a transmission distance of about 120 km with realistic 107 finite data signals and approximately achieve 195 km with 109 signals. Moreover, our proposed protocol is robust against noise in the quantum channel and achieves a threshold error rate of 22.7%. [ABSTRACT FROM AUTHOR]

Quantum illumination protocols can be implemented to improve imaging performance in the low photon flux regime even in the presence of both background light and sensor noise. However, the extent to which this noise can be rejected is limited by the rate of accidental correlations resulting from the detection of photon or noise events that are not quantum-correlated. Here we present an improved protocol that rejects up to ≳ 99.9 % of background light and sensor noise in the low photon flux regime, improving upon our previous results by an order of magnitude. This improvement, which requires no information regarding the scene or noise statistics, will enable extremely low light quantum imaging techniques to be applied in environments previously thought difficult and be an important addition to the development of covert imaging, quantum microscopes, and quantum LIDAR. [ABSTRACT FROM AUTHOR]

Security issues and attack management of optical communication have come increasingly important. Quantum techniques are explored to secure or protect classical communication. In this paper, we present a method for in-service optical physical layer security monitoring that has vacuum-noise level sensitivity without classical security loopholes. This quantum-based method of eavesdropping detection, similar to that used in conventional pilot tone systems, is achieved by sending quantum signals, here comprised of continuous variable quantum states, i.e. weak coherent states modulated at the quantum level. An experimental demonstration of attack detection using the technique was presented for an ideal fibre tapping attack that taps 1% of the ongoing light in a 10 dB channel, and also an ideal correlated jamming attack in the same channel that maintains the light power with excess noise increased by 0.5 shot noise unit. The quantum monitoring system monitors suspicious changes in the quantum signal with the help of advanced data processing algorithms. In addition, unlike the CV-QKD system which is very sensitive to channel excess noise and receiver system noise, the quantum monitoring is potentially more compatible with current optical infrastructure, as it lowers the system requirements and potentially allows much higher classical data rate communication with links length up to 100 s km. [ABSTRACT FROM AUTHOR]

Quantum error-correcting codes play the role of suppressing noise and decoherence in quantum systems by introducing redundancy. Some strategies can be used to improve the parameters of these codes. For example, entanglement can provide a way for quantum error-correcting codes to achieve higher rates than the one obtained by means of the traditional stabilizer formalism. Such codes are called entanglement-assisted quantum error-correcting (EAQEC) codes. In this paper, we utilize algebraic geometry codes to construct several families of EAQEC codes derived from the Euclidean and the Hermitian construction. Three families constructed here consist of codes whose quantum Singleton defect is equal to zero, one, or two. We also construct families of EAQEC codes with an encoding rate exceeding the quantum Gilbert-Varshamov bound. Additionally, asymptotically good towers of linear complementary dual codes are used to obtain asymptotically good families of EAQEC codes consuming maximal entanglement. Furthermore, a simple comparison with the quantum Gilbert-Varshamov bound demonstrates that, by utilizing the proposed construction, it is possible to generate an asymptotically family of EAQEC codes that exceeds this bound. [ABSTRACT FROM AUTHOR]

In this article, we propose a simulation method to investigate the noise mechanism of traveling-wave tube (TWT). Based on the nonlinear theory of Lagrangian description, 1-D noise model is established to analyze the shot noise and the velocity noise of the electron beam in the drift space, which clearly shows that the beam noise propagates along the electron beam with standing wave shape. The shot noise and the velocity noise can be periodically converted into each other along electron beam transmission, which is consistent with the prediction of the classical noise theory developed by Pierce and Danielson (1954). Using the nonlinear beam–wave interaction theory, the evolution process of the shot noise and the velocity noise of the electron beam transforming to the electromagnetic wave in TWT is illustrated. The calculated results show that the input position of the slow wave circuit may affect the noise power spectral density (NPSD) of the device. The proposed method can provide more intuitive and simple images to explain the noise mechanism of TWT. [ABSTRACT FROM AUTHOR]

Two-dimensional quantum walks using a two-state coin have simpler experimental implementation than two-dimensional quantum walks using a four-state coin. However, decoherence occurs inevitably during the evolution of quantum walks due to the coupling between the quantum systems and their environment. Thus, it is interesting to investigate the robustness against decoherence for two- and four-state two-dimensional quantum walks. Here, we investigate the effects of the decoherence on two- and four-state two-dimensional quantum walks produced by the broken-link-type noise and compare their robustness against the broken-link-type noise. Specifically, we analyze the quantum correlation between the two spatial dimensions x and y by using measurement-induced disturbance for the two-state quantum walks, i.e. the alternate walk and the Pauli walk, and the four-state quantum walks, i.e. the Grover, Hadamard and Fourier walks, respectively. Our analysis shows that the two-state walks are more robust against the broken-link-type noise than the four-state walks. [ABSTRACT FROM AUTHOR]

Quantum-limited microwave parametric amplifiers are genuine key pillars for rising quantum technologies and, in general, for applications that rely on the successful readout of weak microwave signals by adding only the minimum amount of noise allowed by quantum mechanics. In this Perspective, after providing a brief overview on the different families of parametric microwave amplifiers, we focus on traveling wave parametric amplifiers, underlining the key achievements of the last few years and the present open challenges. We also discuss possible new research directions beyond amplification such as exploring these devices as a platform for multi-mode entanglement generation and for the development of single photon detectors. [ABSTRACT FROM AUTHOR]

The polarisation Sagnac speedmeter interferometer has the potential to replace the Michelson interferometer as the instrumental basis for future generations of ground-based gravitational wave detectors. The quantum noise benefit of this speedmeter is dependent on high-quality polarisation optics, the polarisation beam-splitter (PBS) and quarter-waveplate (QWP) optics that are key to this detector configuration and careful consideration of the effect of birefringence in the arm cavities of the interferometer. A PBS with an extinction ratio of better than 4000 in transmission and 700 in reflection for a 41° angle of incidence was characterised along with a QWP of birefringence of. The cavity mirror optics of a 10 m prototype polarisation Sagnac speedmeter were measured to have birefringence in the range 1 × 10−3 to 2 × 10−5 radians. This level of birefringence, along with the QWP imperfections, can be cancelled out by careful adjustment of the QWP angle, to the extent that the extinction ratio of the PBS is the leading limitation for the polarisation Sagnac speedmeter in terms of polarisation effects. [ABSTRACT FROM AUTHOR]

Quantum key distribution (QKD) enables two authenticated parties to share secret key and can detect any attack that attempts to eavesdrop on the key. Information reconciliation is an important part of QKD. The secret key between two communication parties can be extracted by correcting errors caused by quantum channel noise. To improve the efficiency of information reconciliation and secret key rate, this paper proposes an improved multidimensional information reconciliation protocol based on systematic polar codes. Moreover, we have demonstrated and analyzed the security of the proposed protocol. Simulation results show that the proposed protocol achieves the reconciliation efficiency of around 97% in a wider range of signal-to-noise ratio range 0 , 0.18 and a quite low frame error rate ( P e < 0.001 ). As a result, the improved multidimensional information reconciliation protocol based on the systematic polar codes can achieve a longer quantum communication transmission distance. [ABSTRACT FROM AUTHOR]

The type of environments to which a quantum system is exposed has a significant impact on the quantum system's entanglement and coherence protection. In this regard, we investigate the time evolution of tripartite entanglement and coherence in GHZ-like state when subject to independent classical environments. In particular, we focus on local environments with the same and mixed disorders, resulting in various Gaussian noisy conditions, namely pure power-law noise, pure fractional Gaussian noise, power-law noise maximized, and fractional Gaussian noise maximized configurations. We show that the environments with mixed disorders are more detrimental than those having single kind of disorder for entanglement and coherence preservation using time-dependent quantum negativity, entanglement witnesses, purity, and decoherence metrics. Besides, there is no ultimate solution for avoiding the negative consequences of fractional Gaussian noise-assisted classical environments in both pure and mixed noise conditions. Not only the noise, but also the number of qubits driven by a certain noise, has been discovered to strongly influence the amount, nature of the decay, and preservation intervals. We also show that the GHZ-like states can be modelled in classical channels driven by pure power-law noise for extended quantum correlations, coherence, and quantum information preservation. In addition, we compare the entanglement measurement efficiency between entanglement witness and negativity measures. [ABSTRACT FROM AUTHOR]

Quantum algorithms offer efficient solutions to computational problems that are expensive to solve classically. Publicly available quantum computers, such as those provided by IBM, can now be used to run small quantum circuits that execute quantum algorithms. However, these quantum computers are highly prone to noise. Here, we introduce important concepts of quantum circuit noise and connectivity that must be addressed to obtain reliable results on quantum computers. We utilize several examples to show how noise scales with circuit depth. We present Simon's algorithm, a quantum algorithm for solving a computational problem of the same name, explain how to implement it in IBM's Qiskit platform, and compare the results of running it both on a noiseless simulator and on physical hardware subject to noise. We discuss the impact of Qiskit's transpiler, which adapts ideal quantum circuits for physical hardware with limited connectivity between qubits. We show that even circuits of only a few qubits can have their success rate significantly reduced by quantum noise unless specific measures are taken to minimize its impact. [ABSTRACT FROM AUTHOR]

• Anatomical noise is the dominant source of image noise in paediatric CBCT. • CNR between fat and muscle was maintained in over 90% of cases for doses ≥1 mGy. • Increasing dose above 1 mGy does not improve image quality or registration accuracy. • Low dose paediatric CBCT protocols are recommended based on the imaging need. Cone beam CT (CBCT) is used in paediatric image-guided radiotherapy (IGRT) for patient setup and internal anatomy assessment. Adult CBCT protocols lead to excessive doses in children, increasing the risk of radiation-induced malignancies. Reducing imaging dose increases quantum noise, degrading image quality. Patient CBCTs also include 'anatomical noise' (e.g. motion artefacts), further degrading quality. We determine noise contributions in paediatric CBCT, recommending practical imaging protocols and thresholds above which increasing dose yields no improvement in image quality. Sixty CBCTs including the thorax or abdomen/pelvis from 7 paediatric patients (aged 6–13 years) were acquired at a range of doses and used to simulate lower dose scans, totalling 192 scans (0.5–12.8 mGy). Noise measured in corresponding regions of each patient and a 10-year-old phantom were compared, modelling total (including anatomical) noise, and quantum noise contributions as a function of dose. Contrast-to-noise ratio (CNR) was measured between fat/muscle. Soft tissue registration was performed on the kidneys, comparing accuracy to the highest dose scans. Quantum noise contributed <20% to total noise in all cases, suggesting anatomical noise is the largest determinant of image quality in the abdominal/pelvic region. CNR exceeded 3 in over 90% of cases ≥ 1 mGy, and 57% of cases at 0.5 mGy. Soft tissue registration was accurate for doses > 1 mGy. Anatomical noise dominates quantum noise in paediatric CBCT. Appropriate soft tissue contrast and registration accuracy can be achieved for doses as low as 1 mGy. Increasing dose above 1 mGy holds no benefit in improving image quality or registration accuracy due to the presence of anatomical noise. [ABSTRACT FROM AUTHOR]

Classical structured light with controlled polarization and orbital angular momentum (OAM) of electromagnetic waves has varied applications in optical trapping, bio-sensing, optical communications and quantum simulations. However, quantum noise and photon statistics of three-dimensional photonic angular momentum are relatively less explored. Here, we develop a quantum framework and put forth the concept of quantum structured light for space-time wavepackets at the single-photon level. Our work deals with three-dimensional angular momentum observables for twisted quantum pulses beyond scalar-field theory as well as the paraxial approximation. We show that the spin density generates modulated helical texture and exhibits distinct photon statistics for Fock-state vs. coherent-state twisted pulses. We introduce the quantum correlator of photon spin density to characterize nonlocal spin noise providing a rigorous parallel with electronic spin noise. Our work can lead to quantum spin-OAM physics in twisted single-photon pulses and opens explorations for phases of light with long-range spin order. Twisted light beams allow unique control of light-matter interaction, but classical models cannot describe this phenomenon at the single-photon level. Here, the quantum state of structured photons is derived instead from quantum field theory which captures the quantum uncertainty in its angular momentum and the non-local photonic spin density correlation. [ABSTRACT FROM AUTHOR]

The simulation of quantum systems on a quantum computer using the Zalka–Wiesner algorithm including quantum noise has been considered. The efficiency of developed methods and algorithms has been demonstrated by example of the solution of the time-dependent Schrödinger equation for a particle in the Pöschl–Teller potential. The developed analytical theory of the effect of quantum noise on the accuracy of simulation has been compared with Monte Carlo simulations. The accuracy of the solution of the Schrödinger equation for a many-electron system has been forecasted as a function of the number of electrons and for different levels of noise. [ABSTRACT FROM AUTHOR]

We have performed a quantum mechanical analysis of travelling-wave parametric amplifiers (TWPAs) in order to investigate five experimental phenomena related to their operations, namely the effect of impedance mismatch, the presence of upper idler modes, the presence of quantum and thermal noise, the generation of squeezed states, and the preservation of pre-squeezed states during amplification. Our analysis uses momentum operators to describe the spatial evolution of quantised modes along a TWPA. We calculate the restriction placed on pump amplitude as well as amplifier gain as a result of impedance mismatch between a TWPA and its external system. We apply our analysis to upper idler modes and demonstrate that they will result in suppressed gain. We show that an ideal TWPA is indeed quantum-limited—i.e. it introduces a half-quantum of zero-point fluctuation which is the minimum possible noise contribution for a phase-preserving linear amplifier. We analyse the thermal noise associated with a TWPA by considering the effect of distributed sources along an amplifier transmission line. Our analysis predicts a doubling of thermal noise in the high gain limit as a result of wave-mixing between signal and idler modes. We study the operation of a TWPA in the presence of a DC bias current, and have shown that highly squeezed states can in principle be generated. However, amplifying a pre-squeezed state using a non-degenerate TWPA generally reduces the squeezing advantage. [ABSTRACT FROM AUTHOR]

In this paper, we demonstrate a method to improve the payoffs of players in relativistic quantum Bayesian game using partial-collapse measurement. We consider two cases. (Only Unruh effect exists, or both Unruh effect and quantum noise are taken into account.) The results show that the payoffs of players can be enhanced greatly in both cases. The payoffs of two players could be above the classical payoffs by choosing the appropriate partial-collapse measurement strengths. It is noted that for the case only Unruh effect exists, the Unruh effect could be eliminated by using partial-collapse measurement and thus the payoffs of two players are almost completely protected. [ABSTRACT FROM AUTHOR]

We investigate the preservation of quantum coherence and entanglement carried by the three non-interacting qubits during their evolution in the presence of an external fluctuating field characterized by a classical Gaussian noise. Initially, the three non-interacting qubits are considered in two different maximally entangled states, namely Greenberger–Horne–Zeilinger ( X G ) and Werner (X W) state. Besides this, we study the time evolution of the two states in three different schemes, namely: common, mixed, and independent system–environment couplings. By deploying different measures, we show that the system–environment coupling and the Gaussian noise greatly affected the quantum correlation and coherence. We also found that the non-local correlation and coherence remain more dominant and robust in common system–environment coupling for the X G state under the Gaussian noise. Hence, this kind of feature of the X G state is a vital resource for the transmission of quantum information with reduced loss. [ABSTRACT FROM AUTHOR]

Quantum key distribution (QKD) is a cryptographic communication protocol that utilizes quantum mechanical properties for provable absolute security against an eavesdropper. The communication is carried between two terminals using random photon polarization states represented through quantum states. Both these terminals are interconnected through disjoint quantum and classical channels. Information reconciliation using delay controlled joint decoding is performed at the receiving terminal. Its performance is characterized using data and error rates. Achieving low error rates is particularly challenging for schemes based on error correcting codes with short code lengths. This article addresses the decoding process using ordered statistics decoding for information reconciliation of both short and medium length Bose–Chaudhuri–Hocquenghem codes over a QKD link. The link's quantum channel is modeled as a binary symmetric quantum depolarization channel, whereas the classical channel is configured with additive white Gaussian noise. Our results demonstrate the achievement of low bit error rates, and reduced decoding complexity when compared to other capacity achieving codes of similar length and configuration. [ABSTRACT FROM AUTHOR]

The theory of spin noise in low-dimensional systems and bulk semiconductors is reviewed. Spin noise is usually detected by optical means continuously measuring the rotation angle of the polarization direction of a probe beam passing through a sample. Spin noise spectra yield rich information about the spin properties of the system, for example, g-factors of the charge carriers, spin relaxation times, parameters of the hyperfine interaction, spin-orbit coupling constants, frequencies and widths of the optical resonances. The review describes basic models of spin noise, methods to theoretically describe it, and thier relation to experimental results. We also discuss the relation between spin noise spectroscopy and strong and weak quantum measurements, as well as spin flip Raman scattering, and analyze similar effects, including manifestations of the charge, current, and valley polarization fluctuations in the optical response. Possible directions for further development of spin noise spectroscopy are outlined. [ABSTRACT FROM AUTHOR]

The dynamics of entanglement measured by concurrence and quantum correlation described by quantum discord under Ornstein-Uhlenbeck noise are investigated in several different cases. Our study mainly found that for both anti-ferromagnetic and ferromagnetic cases, the value of concurrence could be increased significantly by the cooperative effect of XZX+YZY and XZY-YZX three-site interactions. For anti-ferromagnetic case, XZY-YZX interaction has a positive effect on increasing the value of concurrence, nonetheless, for the ferromagnetic case, the XZX+YZY interaction plays a major role in enlarging and sustaining the value of concurrence. Whereas XZY-YZX interaction has a negative effect on concurrence for small J. The Non-Markovian case is much more effective than short-time limit or Markov limit case to preserve both concurrence and quantum discord. For small dissipation, the short-time limit is better than the Markov limit to prolong the lifetime of concurrence and quantum discord. For large dissipation, the Markov limit case is a preferable approximation. The entanglement sudden death time could be prolonged in the ferromagnetic case more than in the anti-ferromagnetic case. [ABSTRACT FROM AUTHOR]

When noisy intermediate scalable quantum (NISQ) devices are applied in information processing, all of the stages through preparation, manipulation, and measurement of multipartite qubit states contain various types of noise that are generally hard to be verified in practice. In this article, we present a scheme to deal with unknown quantum noise and show that it can be used to mitigate errors in measurement readout with NISQ devices. Quantum detector tomography that identifies a type of noise in a measurement can be circumvented. The scheme applies single-qubit operations only, that are with relatively higher precision than measurement readout or two-qubit gates. A classical post-processing is then performed with measurement outcomes. The scheme is implemented in quantum algorithms with NISQ devices: the Bernstein-Vazirani algorithm and a quantum amplitude estimation algorithm in IBMQ _ yorktown and IBMQ _ essex . The enhancement in the statistics of the measurement outcomes is presented for both of the algorithms with NISQ devices. [ABSTRACT FROM AUTHOR]

The mobility of the two-dimensional electron gas (2DEG) in shallow GaAs/ Al x Ga 1 − x As heterostructures is strongly suppressed by unwanted Coulomb scattering from surface charge, likely located in native surface oxides that form after the wafer is removed from the crystal growth system. Here, we show that this native surface oxide can be eliminated by growing an epitaxial aluminum gate before removing the wafer from the growth chamber. We fabricate accumulation mode devices on two wafers with nearly identical structures and growth conditions: one with an epitaxial aluminum gate 35 nm above the channel and another with an ex situ metal gate deposited on an aluminum oxide dielectric. Low temperature transport measurements show that the epitaxial gate design greatly reduces surface charge scattering, with up to 2.5 × increase in mobility. Despite the ultra-shallow 2DEG (35 nm), the mobility remains high even at low carrier densities. Finally, we show that the epitaxial aluminum gate can be patterned to make nanostructures by fabricating a quantum point contact that shows robust and reproducible 1D conductance quantization, with extremely low charge noise. [ABSTRACT FROM AUTHOR]

An atomic magnetometer detects atomic responses to the magnetic field, and its sensitivity is ultimately limited by quantum noise fluctuations. For magnetometers based on nonlinear magneto-optical rotation (NMOR), the possible concurrent generation of light squeezing due to polarization self-rotation complicates the optimization for magnetometer sensitivity. Here, we study NMOR magnetometers with frequency-modulated light in a paraffin coated 87Rb vapor cell in the low and high power regimes corresponding to situations with and without light squeezing, respectively, with detection observables being different Stokes components reflecting the magnetic-field-induced atomic circular dichroism or birefringence. We found that the overall best sensitivity is achieved in the low power regime when there is no light squeezing and for circular dichroism measurement. We provide a general insight on parameter optimization and the choice of detection observables, from the delicate trade-off between the atomic responses and the noises including the technical and quantum optical noises. Our results could have practical significance in optical atomic magnetometry. [ABSTRACT FROM AUTHOR]

Four-wave mixing (FWM) of optical fields has been extensively used in quantum information processing, sensing, and memories. It also forms a basis for nonlinear spectroscopies such as transient grating, stimulated Raman, and photon echo where phase matching is used to select desired components of the third-order response of matter. Here we report an experimental study of the two-dimensional quantum noise intensity difference spectra of a pair of squeezed beams generated by FWM in hot Rb vapor. The measurement reveals details of the χ(3) susceptibility dressed by the strong pump field which induces an AC Stark shift, with higher spectral resolution compared to classical measurements of probe and conjugate beam intensities. We demonstrate how quantum correlations of squeezed light can be utilized as a spectroscopic tool which unlike their classical counterparts are robust to external noise. [ABSTRACT FROM AUTHOR]

We study the behavior of Rényi entropies for pure states from standard assumptions about chaos in the high-energy spectrum of the Hamiltonian of a many-body quantum system. We compute the exact long-time averages of Rényi entropies and show that the quantum noise around these values is exponentially suppressed in the microcanonical entropy. For delocalized states over the microcanonical band, the long-time average approximately reproduces the equilibration proposal of H. Liu and S. Vardhan, with extra structure arising at the order of non-planar permutations. We analyze the equilibrium approximation for AdS/CFT systems describing black holes in equilibrium in a box. We extend our analysis to the situation of an evaporating black hole, and comment on the possible gravitational description of the new terms in our approximation. [ABSTRACT FROM AUTHOR]

We consider the problem of implementing two-party interactive quantum communication over noisy channels, a necessary endeavor if we wish to fully reap quantum advantages for communication. For an arbitrary protocol with n messages, designed for a noiseless qudit channel over a poly (n) size alphabet, our main result is a simulation method that fails with probability less than 2−Θ(nε) and uses a qudit channel over the same alphabet n(1 + Θ (√ε)) times, of which an ε fraction can be corrupted adversarially. The simulation is thus capacity achieving to leading order, and we conjecture that it is optimal up to a constant factor in the √ε term. Furthermore, the simulation is in a model that does not require pre-shared resources such as randomness or entanglement between the communicating parties. Our work improves over the best previously known quantum result where the overhead is a non-explicit large constant [Brassard et al., SICOMP’19] for low ε. [ABSTRACT FROM AUTHOR]

A midfringe locked interferometer with differential detection is proposed for non-contact optical sound measurement, and the equivalent noise level of approximately 0 dB SPL/Hz is achieved. The noise level of the proposed method is 30 dB lower than that of a very recent laser Doppler vibrometer and close to that of a quarter-inch measurement microphone. The midfringe locking stabilizes the optical interferometer against slow environmental fluctuations and enables detection of the acoustic signal directly from optical intensity. The differential detection method eliminates laser intensity noise, which is a dominant noise source in optical interferometers. The noise level of the constructed system was approximately 10 dB above the optical shot-noise (the classical detection limit attributed to the quantum nature of light) at frequencies higher than 2 kHz. Further noise reduction by several available methods could lead to optical measurements that are more sensitive than measurements by microphones. In addition, the constructed interferometer is used to reconstruct sound fields generated by a half-inch laboratory standard microphone used as a transmitter. The proposed method will be a powerful tool for measuring small-amplitude sound fields where it has been challenging to use existing methods. [ABSTRACT FROM AUTHOR]

Using the thermal-entangled state representations, we obtain the analytical evolution of quantum states simultaneously undergoing two kinds of quantum noises that can be represented as the infinitive Kraus operator-sum representation. We also prove the normalization and trace preservation of Kraus operators. Besides, we obtain the evolutions of Wigner distribution and photon number distribution of any quantum state when simultaneously passing through two kinds of quantum noises. [ABSTRACT FROM AUTHOR]

The experimental non-observation of charge-parity (CP) symmetry violation in quantum chromodynamics is commonly referred to as the strong CP problem. The axion, a hypothetical elementary pseudoscalar, is expected to solve the strong CP problem and is also a promising candidate for dark matter. The most sensitive axion search experiments operate at millikelvin temperatures and hence rely on instrumentation that carries signals from a system at cryogenic temperatures to room temperature instrumentation. One of the biggest limiting factors affecting the parameter scanning speed of these detectors is the noise added by the components in the signal detection chain. Since the first amplifier in the chain limits the minimum noise, low-noise amplification is of paramount importance. This paper reports on the operation of a flux-driven Josephson parametric amplifier (JPA) operating at around 2.3 GHz with added noise approaching the quantum limit. The JPA was employed as a first stage amplifier in an experimental setting similar to the ones used in haloscope axion detectors. By operating the JPA at a gain of 19 dB and cascading it with two cryogenic amplifiers operating at 4 K, noise temperatures as low as 120 mK were achieved for the whole signal detection chain. [ABSTRACT FROM AUTHOR]

Quantum machine learning is expected to be one of the potential applications that can be realized in the near future. Finding potential applications for it has become one of the hot topics in the quantum computing community. With the increase of digital image processing, researchers try to use quantum image processing instead of classical image processing to improve the ability of image processing. Inspired by previous studies on the adversarial quantum circuit learning, we introduce a quantum generative adversarial framework for loading and learning a quantum image. In this paper, we extend quantum generative adversarial networks to the quantum image processing field and show how to learning and loading an classical image using quantum circuits. By reducing quantum gates without gradient changes, we reduced the number of basic quantum building block from 15 to 13. Our framework effectively generates pure state subject to bit flip, bit phase flip, phase flip, and depolarizing channel noise. We numerically simulate the loading and learning of classical images on the MINST database and CIFAR-10 database. In the quantum image processing field, our framework can be used to learn a quantum image as a subroutine of other quantum circuits. Through numerical simulation, our method can still quickly converge under the influence of a variety of noises. [ABSTRACT FROM AUTHOR]

The purpose of this work was to assess technical performance of a prototype high-ratio (r29), 80 line cm−1 grid for imaging conditions which mimic those for adult cardiovascular angiography. The standard equipment r15, 80 line cm−1 grid was used as a reference. Plastic Water® LR phantoms with thickness in the range 20–44 cm were used to simulate adult patient attenuation and scatter. Grids were tested using x-ray field of view 20 and 25 cm and x-ray source to detector distance (SID) 107 and 120 cm. The primary transmission fraction (TP) was measured using both narrow beam geometry and a lead beam stop (BS) technique. Scatter transmission (TS) was measured with the lead BS technique. The quantum signal to noise ratio improvement factor (KSNR) was used to describe relative grid performance. The experimental conditions required revised theory to assess grid performance. Theory to account for the detector glare and underestimation of scatter intensity by the lead BS method was developed. Also, novel KSNR theory was developed to allow direct comparison of two grids operated at different SID. Mean TP was modestly lower for the r29 versus r15 grid (0.69 versus 0.75). When tested under equivalent scatter condition, TS of the r29 grid was approximately ˝ that of the r15 grid (0.18 versus 0.34). KSNR of the r29 grid at SID 120 cm compared to the r15 grid at SID 107 cm increased linearly with phantom thickness (range 1.0 to ∼1.16). Findings of this work indicate that the r29 grid used at SID 120 cm is expected to provide improved image quality (or reduced patient radiation dose) when compared to the r15 grid used at SID 107 cm for adult cardiovascular patients and that the potential benefit of the r29 grid increases with patient thickness >20 cm. [ABSTRACT FROM AUTHOR]

Quantum noise stream cipher (QNSC), where signal states are masked by intrinsic quantum noise to directly encrypt data, provides a physical layer security. This paper firstly discusses the security of the QNSC system under the assumption that eavesdropper is restricted to collective attacks. The maximum security capacity for the encrypted data, the running key, and the entire system is derived, respectively. Our simulation results allow a positive information capacity when data transmission distance is no more than 300 km for the number of bases M b = 31 and any mean photon number α 2 by assuming state-of-the-art technology. We find that the security of whole system depends on the security of running key for shorter distances. However, the security of whole system is related to the security of data for longer distances. Furthermore, it is important to improve security of data in QNSC system for longer distances. Besides, this new method proposes a concrete solution for physical encryption systems and paves the way for a wider implementation of the QNSC system. [ABSTRACT FROM AUTHOR]

Objectives: To study how radiologists' perceived ability to interpret digital mammography (DM) images is affected by decreases in image quality. Methods: One view from 45 DM cases (including 30 cancers) was degraded to six levels each of two acquisition-related issues (lower spatial resolution and increased quantum noise) and three post-processing-related issues (lower and higher contrast and increased correlated noise) seen during clinical evaluation of DM systems. The images were shown to fifteen breast screening radiologists from five countries. Aware of lesion location, the radiologists selected the most-degraded mammogram (indexed from 1 (reference) to 7 (most degraded)) they still felt was acceptable for interpretation. The median selected index, per degradation type, was calculated separately for calcification and soft tissue (including normal) cases. Using the two-sided, non-parametric Mann-Whitney test, the median indices for each case and degradation type were compared. Results: Radiologists were not tolerant to increases (medians: 1.5 (calcifications) and 2 (soft tissue)) or decreases (median: 2, for both types) in contrast, but were more tolerant to correlated noise (median: 3, for both types). Increases in quantum noise were tolerated more for calcifications than for soft tissue cases (medians: 3 vs. 4, p = 0.02). Spatial resolution losses were considered less acceptable for calcification detection than for soft tissue cases (medians: 3.5 vs. 5, p = 0.001). Conclusions: Perceived ability of radiologists for image interpretation in DM was affected not only by image acquisition-related issues but also by image post-processing issues, and some of those issues affected calcification cases more than soft tissue cases. Key Points: • Lower spatial resolution and increased quantum noise affected the radiologists' perceived ability to interpret calcification cases more than soft tissue lesion or normal cases. • Post-acquisition image processing-related effects, not only image acquisition-related effects, also impact the perceived ability of radiologists to interpret images and detect lesions. • In addition to current practices, post-acquisition image processing-related effects need to also be considered during the testing and evaluation of digital mammography systems. [ABSTRACT FROM AUTHOR]

The quantum capacity of a noisy quantum channel determines the maximal rate at which we can code reliably over asymptotically many uses of the channel, and it characterizes the channel’s ultimate ability to transmit quantum information coherently. In this paper, we derive single-letter upper bounds on the quantum and private capacities of quantum channels. The quantum capacity of a quantum channel is always no larger than the quantum capacity of its extended channels, since the extensions of the channel can be considered as assistance from the environment. By optimizing the parametrized extended channels with specific structures such as the flag structure, we obtain new upper bounds on the quantum capacity of the original quantum channel. Furthermore, we extend our approach to estimating the fundamental limits of private communication and one-way entanglement distillation. As notable applications, we establish improved upper bounds to the quantum and private capacities for fundamental quantum channels of interest in quantum information, some of which are also the sources of noise in superconducting quantum computing. In particular, our upper bounds on the quantum capacities of the depolarizing channel and the generalized amplitude damping channel are strictly better than previously best-known bounds for certain regimes. [ABSTRACT FROM AUTHOR]

A double‐mode strategy of coherent quantum noise cancellation (CQNC) is developed to mitigate the effect of the backaction‐noise in optomechanical systems. Working under an asymmetrical configuration, the CQNC strategy of quantum interference can promote the system stabilization in addition to enhance its sensitivity in weak‐force metrology by offsetting the backaction‐noise. Through exploiting the coupling between the probe mode and the ancillary mode, the rotating‐wave term and the counter‐rotating term are found to be responsible under certain circumstances for system‐stability and noise‐suppression, respectively. They demonstrate a subtle compromise between the resonant noise cancellation ratio and the effective damping rate. This strategy can be carried out in optomechanical setups with a membrane in the middle or a twisted‐cavity‐based weak‐torque detector. [ABSTRACT FROM AUTHOR]

10.1088/0256-307x/33/10/103701 7 P. Dubé, A. A. Madej, A. Shiner, and B. Jian, "88Sr+ single-ion optical clock with a stability approaching the quantum projection noise limit", Phys. The rf voltage amplitude has been calculated to fit published secular frequencies (for the clock ion species) used in current optical clocks. [Extracted from the article]

Quantum Bernoulli noises (QBN) are the family of annihilation and creation operators acting on Bernoulli functionals, which satisfy a canonical anti-commutation relation in equal-time. In this paper, we aim to investigate quantum Feller semigroups in terms of QBN. We first investigate local structure of the algebra generated by identity operator and QBN. We then use our new results obtained here to construct a class of quantum Markov semigroups from QBN which enjoy Feller property. As an application of our results, we examine a special quantum Feller semigroup associated with QBN, when it reduced to a certain Abelian subalgebra, the semigroup gives rise to the semigroup generated by Ornstein–Uhlenbeck operator. Finally, we find a sufficient condition for the existence of faithful invariant states that are diagonal for the semigroup. [ABSTRACT FROM AUTHOR]

Optically controlled self-assembled quantum dots have received substantial attention in the quantum computing area, as techniques for initializing, manipulating, and reading out single spin qubits have been demonstrated in essence. The electron-spin coherence and hole-spin coherence are limited due to noisy quantum effects, and there is a significant need for further evaluation and investigation studies. In this work, the behavior of charge noise and spin noise for a fundamental logic unit of four qubit embedded in an AlAs/GaAs heterostructure is reported based on the modeling and simulation approach in the atomic level to provide a more in-depth analysis and evaluation of quantum noise. The numerical calculations are based on reliable simulation methods, which are consistent with experimental results. The approach presented here can become the basis for scaled-up advanced simulations expanding to larger logical blocks of qubits. [ABSTRACT FROM AUTHOR]

Entanglement is one of essential quantum resources in quantum information processing, playing an important role during quantum communication and computation. While any system unavoidably interacts with its surrounding environment, this thus will result in decoherence or dissipation effect. With this in mind, a natural question arises: how to recover quantum entanglement under decoherence inducing by the environmental noises. In this work, our attempt is to propose an effective strategy to optimally achieve entanglement recovery. Specifically, we derive a nontrivial condition satisfied by any operation U, i.e. , which will definitely recover the entanglement of an arbitrary two-qubit system, and more importantly offer an explicit physical explanation towards the intrinsic mechanics of the entanglement recovery. By means of derivations, we obtain the appropriate operational strength to realize optimal entanglement recovery through taking advantage of our proposed methods. As illustrations, we apply some local operations complying with our presented strategy on validly protecting entanglement, including -symmetry operation, quantum weak measurement and quantum reversal measurement. [ABSTRACT FROM AUTHOR]

In the last few decades, much effort has been made for the production of squeezed vacuum states in order to reduce quantum noise in the audio-frequency band. This technique has been implemented in all running gravitational-wave interferometric detectors and helped to improve their sensitivity. While the detectors are acquiring data for astrophysical observations, they must be kept in the operating condition, also called "science mode," that is, a state that requires the highest possible duty-cycle for all the instrumental parts and controls. We report the development of a highly automated setup for the generation of optical squeezed states, where all the required control loops are supervised by a software based on finite state machines; we took special care to grant ease of use, stability of operation, and possibility of auto-recovery. Moreover, the setup has been designed to be compatible with the existing software and hardware infrastructure of the Virgo detector. In this paper, we discuss the optical properties of this squeezing setup, the locking techniques, and the automation algorithms. [ABSTRACT FROM AUTHOR]

This paper proposed a novel dynamic quantum secret sharing protocol in high-dimensional quantum system. Via transmitting the particles circularly and local unitary operations, the dealer and all agents can share the multi-particle entangled GHZ state in high-dimensional quantum system. The proposed protocol allows a dealer to share the predetermined dits without directly distributing any piece of shares to agents. To recover the secrets, dealer and all agents only need to perform the single-particle measurement operation and then implement the simple modular arithmetic operation according to their corresponding measurement results. Besides, in the proposed protocol, only a little fraction of entangled GHZ states are employed for eavesdropping check instead of lots of decoy (or detecting) particles used in previous protocols. Since the protocol is designed in the high-dimensional quantum system, it makes our protocol have higher resource capacity and better security in detecting the illegal eavesdropper than former protocols designed in two-dimensional quantum system. Security analyses indicate that the proposed protocol is immune to general attacks of intercept-and-resend, entangle-and-measure, collusion, and revoked a dishonest agent. Furthermore, the efficiency of proposed DQSS protocol in noise environment is deduced through quantum fidelity. The obtained results indicate that the efficiency of proposed protocol decreases with the increase in channel noise parameter and it has a quite different efficiency in four types of noise, i.e., dit-flip, d-phase-flip, amplitude-damping and depolarizing. [ABSTRACT FROM AUTHOR]

This paper takes advantage of the quantum mechanics to present two efficient circular controlled quantum communication schemes. The proposed protocols utilize ten qubits for transmitting the information qubits to five partners circularly, under the permission of a controller. The first protocol is a circular controlled quantum teleportation, which teleports unknown quantum states. The second protocol is a circular controlled quantum broadcast scheme which sends quantum states to two dispersed recipients, circularly. In this paper, the effects of quantum noises on these protocols are analyzed, and the fidelity of the quantum states is calculated too. We will see that, in the circular controlled quantum teleportation protocol, the impact of the noise on input qubits is less than its impact on channel qubits. [ABSTRACT FROM AUTHOR]

In this paper, we propose a reduced-form model to price default risk in mortgages and fixed-rate pass-through mortgage-backed securities. Since the default of borrowers is often affected by macroeconomic conditions, we take into account the changes of market regimes. We introduce a default factor process to model the default risk of borrowers and define its exponential decreasing rate as default rate, which follows a shot-noise process. The model assumes that the interest rate and the default rate are all influenced by macroeconomic conditions described by a homogeneous Markov chain. Explicit pricing formulas for mortgage-backed securities with defaultable underlying mortgages are obtained through the conditional Laplace transform of the regime-switching shot-noise process. Numerical illustration is also presented to show the impact of model parameters on the price. [ABSTRACT FROM AUTHOR]

We consider the estimation of an arbitrary parameter φ, such as the temperature or a magnetic field, affecting in a distributed manner the components of an arbitrary linear optical passive network, such as an integrated chip. We demonstrate that Heisenberg scaling precision (i.e. of the order of 1/N, where N is the number of probe photons) can be achieved without any iterative adaptation of the interferometer hardware and by using only a simple, single, squeezed light source and well-established homodyne measurements techniques. Furthermore, no constraint on the possible values of the parameter is needed but only a preliminary shot-noise estimation (i.e. with a precision of) easily achievable without any quantum resources. Indeed, such a classical knowledge of the parameter is enough to prepare a single, suitable optical stage either at the input or the output of the network to monitor with Heisenberg-limited precision any variation of the parameter to the order of without the need to iteratively modify such a stage. [ABSTRACT FROM AUTHOR]

Imperfections in practical detectors, including limited detection efficiency, and inherent electronic noise, can seriously decrease the transmission distance of continuous-variable measurement-device-independent quantum key distribution systems. Owing to the difficulties inherent in realizing a high-efficiency fiber homodyne detector, challenges still exist in continuous-variable measurement-device-independent quantum key distribution system implementation. We offer an alternative approach in an attempt to solve these difficulties and improve the potential for system implementation. Here, a novel practical detector modeling method is utilized, which is combined with a one-time shot-noise-unit calibration method for the purpose of system realization. The new modeling method benefits greatly from taking advantage of one-time shot-noise-unit calibration methods, such as measuring electronic noise and shot noise directly to a novel shot-noise unit, so as to eliminate the statistical fluctuations found in previous methods; this makes the implementation of such systems simpler, and the calibration progress more accurate. We provide a simulation of the secret key rate versus distance with different parameters. In addition, the minimal detection efficiency required at each distance, as well as the contrast between the two methods, are also shown, so as to provide a reference in terms of system realization. [ABSTRACT FROM AUTHOR]

In this paper, we investigate the effects of three single‐qubit quantum noise channels on the quantum nonlinear search algorithm proposed by Abrams and Lloyd. We focus on the gates of the nonlinear part of the algorithm and consider the case where the quantum noise channel only affects the qubit on which the gate is proceeding. Assuming that quantum noise effects occur after using the gates of the nonlinear part of the algorithm, we find that the quantum nonlinear search algorithm appears to be very resilient to the quantum noise when the desired state does not exist in the first register and is subject to the phase damping channel or the depolarising channel. In this paper the effects of three single‐qubit quantum noise channels on the quantum nonlinear search algorithm proposed by Abrams and Lloyd are investigated. The focus is set on the gates of the nonlinear part of the algorithm by considering the case where the quantum noise channel only affects the qubit on which the gate is proceeding. Assuming that quantum noise effects occur after using the gates of the nonlinear part of the algorithm, it is found that the quantum nonlinear search algorithm appears to be very resilient to the quantum noise when the desired state does not exist in the first register and is subject to the phase damping channel or the depolarising channel. [ABSTRACT FROM AUTHOR]