Search

Squeezed reservoir engineering is a powerful technique in quantum information that combines the features of squeezing and reservoir engineering to create and stabilize non-classical quantum states. In this paper, we focus on the previously neglected aspect of the impact of the squeezing phase on the precision of quantum phase and amplitude estimation based on a simple model of a two-level system (TLS) interacting with a squeezed reservoir. We derive the optimal squeezed phase-matching conditions for phase ϕ and amplitude θ parameters, which are crucial for enhancing the precision of quantum parameter estimation. The robustness of the squeezing-enhanced quantum Fisher information against departures from these conditions is examined, demonstrating that minor deviations from phase-matching can still result in remarkable precision of estimation. Additionally, we provide a geometric interpretation of the squeezed phase-matching conditions from the classical motion of a TLS on the Bloch sphere. Our research contributes to a deeper understanding of the operational requirements for employing squeezed reservoir engineering to advance quantum parameter estimation. [ABSTRACT FROM AUTHOR]

In the field of Internet, an image is of great significance to information transmission. Meanwhile, how to ensure and improve its security has become the focus of international research. We combine DNA codec with quantum Arnold transform (QArT) to propose a new double encryption algorithm for quantum color images to improve the security and robustness of image encryption. First, we utilize the biological characteristics of DNA codecs to perform encoding and decoding operations on pixel color information in quantum color images, and achieve pixel-level diffusion. Second, we use QArT to scramble the position information of quantum images and use the operated image as the key matrix for quantum XOR operations. All quantum operations in this paper are reversible, so the decryption operation of the ciphertext image can be realized by the reverse operation of the encryption process. We conduct simulation experiments on encryption and decryption using three color images of "Monkey", "Flower", and "House". The experimental results show that the peak value and correlation of the encrypted images on the histogram have good similarity, and the average normalized pixel change rate (NPCR) of RGB three-channel is 99.61%, the average uniform average change intensity (UACI) is 33.41%, and the average information entropy is about 7.9992. In addition, the robustness of the proposed algorithm is verified by the simulation of noise interference in the actual scenario. [ABSTRACT FROM AUTHOR]

We investigated the quantum speed limit (QSL) time of a spin qubit coupled to an XXZ Heisenberg spin chain environment. The spins of the environment are coupled to the system qubit through Heisenberg like interaction. We carried out our investigations under approximate solution and we evaluate the minimal evolution time from initial state to one of its final target state. QSL time becomes uniform in the low temperature limit and at higher temperature different oscillatory behaviors are observed. Maximal speed of evolution of quantum systems is determined by QSL time. We use Margolus-Levitin (ML) types bound to investigate the minimal evolution time of quantum states. We also discuss the dependence of QSL time upon temperature, driving time and anisotropy of spin chain environment. [ABSTRACT FROM AUTHOR]

The purpose of this article is to further investigate the assisted cloning of a d-dimensional arbitrary unknown state by utilizing quantum teleportation (QT) and remote state preparation (RST) techniques. We first propose a scheme for cloning an arbitrary unknown single-qudit state with assistance from a state preparer. In this scheme, the maximally and non-maximally bipartite d-dimensional states are used as quantum channels, respectively. In the first stage of scheme requires usual QT and in the second stage, the state preparer disentangles the left over entangled states by introducing one auxiliary qudit and performing a generalized CNOT, a single-qudit positive operator-valued measurement (POVM) and a single-qudit projective measurement process and conveys some classical messages to different parties so that a copy is produced probabilistically with the unit fidelity. Then by replacing the maximally or non-maximally bipartite d-dimensional entangled channel with a sequence of maximally or non-maximally bipartite d-dimensional entangled states as a quantum channel, we can extend the above scheme to the case of cloning a d-dimensional arbitrary unknown m-qudit state with the unit fidelity and a certain probability in the help of the state preparer. [ABSTRACT FROM AUTHOR]

We study the exceptional-point (EP) structure and the associated quantum dynamics in a system consisting of a non-Hermitian qubit and a Hermitian qubit. We find that the system possesses two sets of EPs, which divide the system-parameter space into P T -symmetry unbroken, partially broken and fully broken regimes, each with distinct quantum-dynamics characteristics. Particularly, in the partially broken regime, while the P T -symmetry is generally broken in the whole four-dimensional Hilbert space, it is preserved in a two-dimensional subspace such that the quantum dynamics in the subspace are similar to those in the P T -symmetry unbroken regime. In addition, we reveal that the competition between the inter-qubit coupling and the intra-qubit driving gives rise to a complex pattern in the EP variation with system parameters. [ABSTRACT FROM AUTHOR]

Controlled quantum teleportation (CQT) can be considered as a variant of quantum teleportation in which three parties are involved where one party acts as the controller. The usability of the CQT scheme depends on two types of fidelities viz. conditioned fidelity and non-conditioned fidelity. The difference between these fidelities may be termed as power of the controller and it plays a vital role in the CQT scheme. Thus, our aim is to estimate the power of the controller in such a way so that its estimated value can be obtained in an experiment. To achieve our goal, we have constructed a witness operator and have shown that its expected value may be used in the estimation of the lower bound of the power of the controller. Furthermore, we have shown that it is possible to make the standard W state useful in the CQT scheme if one of its qubits either passes through the amplitude damping channel or the phase damping channel. We have also shown that the phase damping channel performs better than the amplitude damping channel in the sense of generating more power of the controller in the CQT scheme. [ABSTRACT FROM AUTHOR]

This paper explores a double quantum images representation (DNEQR) model that allows for simultaneous storage of two digital images in a quantum superposition state. Additionally, a new type of two-dimensional hyperchaotic system based on sine and logistic maps is investigated, offering a wider parameter space and better chaotic behavior compared to the sine and logistic maps. Based on the DNEQR model and the hyperchaotic system, a double quantum images encryption algorithm is proposed. Firstly, two classical plaintext images are transformed into quantum states using the DNEQR model. Then, the proposed hyperchaotic system is employed to iteratively generate pseudo-random sequences. These chaotic sequences are utilized to perform pixel value and position operations on the quantum image, resulting in changes to both pixel values and positions. Finally, the ciphertext image can be obtained by qubit-level diffusion using two XOR operations between the position-permutated image and the pseudo-random sequences. The corresponding quantum circuits are also given. Experimental results demonstrate that the proposed scheme ensures the security of the images during transmission, improves the encryption efficiency, and enhances anti-interference and anti-attack capabilities. [ABSTRACT FROM AUTHOR]

In this paper we describe remote state preparation schemes for a qubit through quantum walks on a line, a cycle and on a two-vertex complete graph. In all these three cases, there is no requirement for shared quantum entangled channels, which precludes the possibility of disturbances created by noisy environments. The state intended for remote preparation, although known to the intender, is not in the physical possession of any of the involved parties. The protocol proposed here is a perfect communication protocol. [ABSTRACT FROM AUTHOR]

Quantum secret sharing (QSS) is one of the basic communication primitives in future quantum networks which addresses part of the basic cryptographic tasks of multiparty communication and computation. Nevertheless, it is a challenge to provide a practical QSS protocol with security against general attacks. A QSS protocol that balances security and practicality is still lacking. Here, we propose a QSS protocol with simple phase encoding of coherent states among three parties. Removing the requirement of impractical entangled resources and the need for phase randomization, our protocol can be implemented with accessible technology. We provide the finite-key analysis against coherent attacks and implement a proof-of-principle experiment to demonstrate our scheme’s feasibility. Our scheme achieves a key rate of 85.3 bps under a 35 dB channel loss. Combined with security against general attacks and accessible technology, our protocol is a promising candidate for practical multiparty quantum communication networks. [ABSTRACT FROM AUTHOR]

Finding a minimum is a fundamental calculation in many quantum algorithms. However, challenges are faced in demonstrating it effectively in real quantum computers. In practice, the number of solutions is unknown, and there is no universal encoding method. Besides that, current quantum computers have limited resources. To alleviate these problems, this paper proposes a general quantum minimum searching algorithm. An adaptive estimation method is adopted to calculate the number of solutions, and a quantum encoding circuit for arbitrary databases is presented for the first time, which improves the universality of the algorithm and helps it achieve a nearly 100% success rate in a series of random databases. Moreover, gate complexity is reduced by our simplified Oracle, and the realizability of the algorithm is verified on a superconducting quantum computer. Our algorithm can serve as a subroutine for various quantum algorithms to promote their implementation in the Noisy Intermediate-Scale Quantum era. k]quantum minimum searching algorithm k]quantum circuit k]superconducting quantum computer k]quantum encoding [ABSTRACT FROM AUTHOR]

The nuclear system is a promising area for demonstrating practical quantum advantage. A comprehensive computation of a nuclear system in a classical computer is beyond the capacity of current classical computers. With the rapid development of hardware, the prospect of using quantum computers in nuclear physics is close at hand. In this paper, we report a full quantum package, QCSH, for solving a nuclear shell model in a quantum computer. QCSH uses the linear combination of the unitary formalism of quantum computing and performs all calculations in a quantum computer. The complexities of qubit resource and the number of basic gates of QCSH are both polynomials to the number of nucleons in nuclei. For example, QCSH is used to calculate the binding energies of 12 light nuclei (i.e., 2H, 3H, 3He, 4He, 6Li, 7Li, 12C, 14N, 16O, 17O, 23Na, and 40Ca). Moreover, we experimentally demonstrate the calculation of deuteron binding energy using a superconducting quantum processor. The result indicates that QCSH can provide meaningful results already in near-term quantum devices. [ABSTRACT FROM AUTHOR]

Bidirectional quantum teleportation is a fundamental protocol for exchanging quantum information between two quantum nodes. Till now, all bidirectional quantum teleportation protocols have achieved a maximum efficiency of 40 % . Here, we propose a new scheme for a symmetric bidirectional quantum teleportation using a six-qubit cluster state as the quantum channel, for symmetric ( 3 ↔ 3 ) qubit bidirectional quantum teleportation of a special three-qubit entangled state. The novelty of our scheme lies in its generalisation for ( N ↔ N ) qubit bidirectional quantum teleportation employing a 2N-qubit cluster state. The efficiency of the proposed protocol is remarkably increased to 50 % which is the highest till now. Interestingly, only GHZ-state measurements and four Toffoli-gate operations are necessary which is independent of the number (N) of qubits to be teleported. [ABSTRACT FROM AUTHOR]

Let H be a separable complex Hilbert space. The aim of this paper is to extend some properties of fidelity from finite to the infinite-dimensional Hilbert spaces. Firstly, we give two characterizations about fidelity between two positive trace-class operators. Then the strong concavity, monotonicity of fidelity and the Alberti’s theorem are given in infinite-dimensional case. At last, we present a direct proof of Uhlmann’s theorem. [ABSTRACT FROM AUTHOR]

We investigate the effects of temperature on quantum Fisher information (QFI), fidelity, and entropy squeezing in two interacting superconducting qubits (SCQs). We show how the variations in these quantum quantifiers may be controlled by carefully selecting the model's physical parameters (PPM). We obtain a trapping phenomena for Fisher information, allowing us to improve the QFI and retain the amount of information while also preserving it from information loss due to temperature impacts. We evaluate the fidelity of the SCQ to explain the dynamic aspects of the QFI in relation to the PPM. Furthermore, we examine the influence of the PPM on the variation in the squeezing entropy for SCQs. The results indicate how, in terms of quantum measurement theory, the system under consideration might be valuable in enabling the realization of experiments under optimal conditions.

Deformed Jaynes–Cummings model (JCM) has a physical importance in quantum optics. Hence, we investigated the nonlinear JCM including the intensity-dependent coupling constant and the additional Kerr term. The cavity was assumed to be in thermal equilibrium with a heat reservoir at temperature T. Using the generators of a closed algebra which reduces to the su(1, 1) and Heisenberg–Weyl algebras at limiting cases, and considering the total excitation number as a constant of motion, the total Hilbert space decomposes into two subspaces. So the eigenvalues and the corresponding eigenvectors were obtained. We derived the thermal density matrix and analysed the fidelity and thermal entanglement using negativity measure. Furthermore, we studied the Berry phase of the nonlinear atom–field system and explored the influence of nonlinearity on the quantum phase transition (QPT) point and entanglement. It is found that the deformation parameter can strongly affect the fidelity, negativity and QPT point. [ABSTRACT FROM AUTHOR]

Sequential sharing of nonlocal correlation is inherently related to its application. We address the question as to how many observers can share the nonlocal advantage of quantum coherence (NAQC) in a (d × d)-dimensional state, where d is a prime or a power of a prime. We first analyze the trade-off between disturbance and information gain of the general d-dimensional unsharp measurements. Then in a scenario where multiple Alices perform unsharp measurements on one party of the state sequentially and independently and a single Bob measures coherence of the conditional states on the other party, we show that at most one Alice can demonstrate NAQC with Bob. This limit holds even when considering the weak measurements with optimal pointer states. These results may shed light on the interplay between nonlocal correlations and quantum measurements on high-dimensional systems and the hierarchy of different quantum correlations. [ABSTRACT FROM AUTHOR]

A salient merit of processing quantum information is the ability of simultaneously working with both bit zero and bit one. The basic unit of quantum information, the so-called qubit, is a superposition of two orthogonal (or near-orthogonal) quantum states which can be realised on distinct physical platforms. At present, no unique qubit encoding exists that is superior to all the other ones. Different labs are implementing their most convenient technique for encoding the qubit and so the network of labs becomes heterogeneous. In this paper, we consider two types of qubit encodings, one is the single-rail qubit in terms of discrete-variable (DV) states 0 and 1 which are respectively the vacuum and the single-photon state and the other is the coherent-state qubit in terms of continuous-variable (CV) states α and - α which are coherent states with equal amplitudes but opposite phases. We devise linear-optics schemes to teleport one type of qubit to the other type. More than that, our teleportation schemes are designed so that two kinds of controllers, one is capable of manipulating single-rail qubits (DV controller) while the other coherent-state ones (CV controller), are able to simultaneously supervise the tasks in both directions. We first propose a quantum circuit to prepare a relevant four-party pure entangled state serving as a quantum channel between the four participants: two teleporters and two controllers. We then detail the hybrid controlled teleportation protocols taking into account the dissipation effect caused by the presence of losses in the environment surrounding the participants. [ABSTRACT FROM AUTHOR]

Vectorial fields such as the electromagnetic field are commonly employed for codifying both qubits and information. It is considered as a three-qubits Heisenberg chain with multiple interaction in the presence of a scalar field, as it is the temperature field. The corresponding pairwise thermal entanglement is calculated. Our results corroborate with the results of Yang and Huang, Quant. Inf. Proc.16:281 (2017). To first order of approximation in powers of β = 1 / T , it is shown that a temperature field can codify entanglement. A scalar field substrate can be used to distribute quantum entanglement in communication protocols that require this ingredient. Present results can be extrapolated to other physical systems such as Heisenberg spins (two-site) or superconducting qubits, provided the respective quantum correlation (entanglement or discord) expression depends explicitly on the temperature scalar field. [ABSTRACT FROM AUTHOR]

In this paper, we propose a new theoretical scheme for quantum secure direct communication (QSDC) with user authentication. Different from the previous QSDC protocols, the present protocol uses only one orthogonal basis of single-qubit states to encode the secret message. Moreover, this is a one-time and one-way communication protocol, which uses qubits prepared in a randomly chosen arbitrary basis, to transmit the secret message. We discuss the security of the proposed protocol against some common attacks and show that no eavesdropper can get any information from the quantum and classical channels. We have also studied the performance of this protocol under realistic device noise. We have executed the protocol in IBMQ Armonk device and proposed a repetition code based protection scheme that requires minimal overhead. [ABSTRACT FROM AUTHOR]

In this paper, the concept of nested multilevel entanglement is studied and formulated in terms of Matryoshka states. The generation of Matryoshka quantum resource states, which contain nested entanglement patterns, based on an anisotropic XY spin–spin interaction-based model has been proposed. Other classes of nested entanglement, such as in Matryoshka generalised GHZ states and Matryoshka Q-GHZ states, are studied. Generation, characterisation and application of a genuinely entangled seven-qubit resource state close to being a Matryoshka Q-GHZ states is explored, with theoretical schemes for quantum teleportation of arbitrary one-, two- and three-qubits states, bidirectional teleportation of arbitrary two-qubit states and probabilistic circular controlled teleportation proposed for the state. Fractal network protocols, surface codes and graph states as well as generation of arbitrary entangled states at remote locations are also discussed, to highlight the importance of this class of quantum states. [ABSTRACT FROM AUTHOR]

As an important technology of the quantum detection, the quantum synchronization detection is always used in the detection or measurement of some quantum systems. A probing model is established to describe the probing of a qubit system in the cavity field and to reveal the effect of the environment (cavity) on the quantum synchronization occurrence, as well as the interactions among environment, a qubit system, and probing equipment. By adjusting the frequency of the probe, the in-phase, anti-phase, and out-of-phase synchronization can be achieved. Simultaneously, the effect of γ 3 ${\gamma }_{3}$ which describes the interaction strength between the probe and environments for quantum synchronization is discussed under different Ohmic dissipation index s. Finally, the machine learning method is applied to present an optimization for classification and regression of synchronization transition dependent on s and γ 3 ${\gamma }_{3}$. [ABSTRACT FROM AUTHOR]

We quantify the entanglement and its variations via generalized concurrence, Meyer–Wallach measure and its generalizations. Then we investigate the interactions between qubits on complete graphs, tree graphs, chain graphs and loop graphs with 3 to 8 qubits. It is observed that the amount of all entanglement measures in tree graph in the first group of considered graphs, are equal. The complete equivalent graph is equal and the entanglement measures for these graphs change altering the number of qubits. Furthermore, it can be seen that the entanglement measures are increased augmenting the number of qubits in the chain graph and loop graph. The entanglement of loop graphs is equal to or greater than the entanglement of chain graphs assuming the same number of qubits. Also there is a significant relation between entanglement, number of qubits, and interactions between qubits for the second group of considered graphs. As the number of interactions (presented by edges) increases between the qubits, the entanglements increase in these states. It is shown that the employed entanglement measures reveal the different values changing the number of qubits (vertices). [ABSTRACT FROM AUTHOR]

A quantum network is a promising quantum many-body system because of its tailored geometry and controllable interaction. Here, we propose an external control scheme for the qubit-photon interaction and multiqubit reset in a dissipative quantum network, which comprises superconducting circuit chains with microwave drives and filter-filter couplings. The traditional multiqubit reset of the quantum network requires physically disconnected qubits to prevent their entanglement. However, we use an original effect of dissipation, i.e., consuming the entanglement generated by qubits' interaction, to achieve an external control of the multiqubit reset in an always-connected superconducting circuit. The reset time is independent of the number of qubits in the quantum network. Our proposal can tolerate considerable fluctuations in the system parameters and can be applicable to higher-dimensional quantum networks. [ABSTRACT FROM AUTHOR]

We propose the optimal economical telecloning of equatorial qubits. The fidelity of each copy is optimal, and the telecloning can be realized with the success probability 100%. The efficiency of telecloning is much better than the protocol in the previous contributions (Wang and Yang in Phys Rev A 79:062315, 2009). [ABSTRACT FROM AUTHOR]

In this note we compare the views of Bohr (known as the Copenhagen interpretation of quantum mechanics) with the views of Bell: complementarity versus nonlocality.

Relativistic invariance is a physical law verified in several domains of physics. The impossibility of faster than light influences is not questioned by quantum theory. In quantum electrodynamics, in quantum field theory and in the standard model relativistic invariance is incorporated by construction. Quantum mechanics predicts strong long range correlations between outcomes of spin projection measurements performed in distant laboratories. In spite of these strong correlations marginal probability distributions should not depend on what was measured in the other laboratory what is called shortly: non-signalling. In several experiments, performed to test various Bell-type inequalities, some unexplained dependence of empirical marginal probability distributions on distant settings was observed. In this paper we demonstrate how a particular identification and selection procedure of paired distant outcomes is the most probable cause for this apparent violation of no-signalling principle. Thus this unexpected setting dependence does not prove the existence of superluminal influences and Einsteinian no-signalling principle has to be tested differently in dedicated experiments. We propose a detailed protocol telling how such experiments should be designed in order to be conclusive. We also explain how magical quantum correlations may be explained in a locally causal way.

In this paper, we put forward a scheme to realise joint remote state preparation (JRSP) of an arbitrary eight-qubit cluster-type state with two non-maximally entangled Greenberger–Horne–Zeilinger (GHZ) states in a recursive manner. The senders begin by helping the remote receiver to construct one intermediate state which is related to the target state closely. Then, the receiver introduces auxiliary qubits and applies appropriate local operations to obtain the target eight-qubit cluster-type state. It is shown that one new GHZ channel can be distributed among three participants with a certain probability if the initial attempt fails. Moreover, compared with the previous protocols, in our scheme both quantum resources and classical communications are considerably reduced. [ABSTRACT FROM AUTHOR]

We study a scheme for generating continuous variable tripartite entanglement of two mirrors and the reflecting field of a ring cavity. We find that significant entanglement can be generated with shot-noise-limited driving field, and the squeezing property of the driving field can enhance the entanglement. We also show the entanglement is generated over a wide range of analysis frequency and temperatures of the environment, which is experimentally accessible. This system may be potentially useful for quantum information processing and quantum networks. [ABSTRACT FROM AUTHOR]

Quantum privacy query (QPQ) is a cryptographic application that protects the privacy of both users and databases while querying the database secretly. In most existing QPQ protocols, the protection of user privacy can only be cheat-sensitive. Cheat-sensitive means that Bob will be found later with a certain probability if he tries to get the address queried by Alice. On the premise of cheat-sensitive, although Alice can discover Bob's malicious behavior after a query (transaction), the secret information of Alice was leaked in the completed query, which is likely to be a fatal blow to Alice. Or, to prevent Bob's malicious behavior, Alice executes one or more additional queries to test Bob's honesty. However, to bypass Alice's honesty test, Bob can also provide several honest queries before performing dishonest queries. Therefore, cheat-sensitive should not be the ultimate goal of user privacy protection in QPQ. In this paper, we propose a two-way QKD-based QPQ protocol with better user privacy protection than cheat-sensitive based on order rearrangement of qubits. The proposed QPQ protocol can resist the Trojan horse attack even without wavelength filter and photon number splitter equipped with auxiliary monitoring detectors. [ABSTRACT FROM AUTHOR]

The Wigner representation of parametric down conversion in the Heisenberg picture is applied to the study of the Rome teleportation experiment. We investigate the physical meaning of the zeropoint inputs at the different areas of the experimental set-up. In particular, we establish a quantitative relationship between the zeropoint sets of modes that are needed for the preparation of the quantum state to be teleported, the idle channels inside the one-photon polarization-momentum Bell-state analyser, and the possibility of performing teleportation of a polarization state with certainty. [ABSTRACT FROM AUTHOR]

The Tietz-Hua potential is modified by the inclusion of DeCh-11-Che-bhr-rebe-bhr-re term to the Tietz-Hua potential model since a potential of such type is very good in the description and vibrational energy levels for diatomic molecules. The energy eigenvalues and the corresponding eigenfunctions are explicitly obtained using the methodology of parametric Nikiforov-Uvarov. By putting the potential parameter b=0, in the modified Tietz-Hua potential quickly reduces to the Tietz-Hua potential. To show more applications of our work, we have computed the Shannon entropy and Information energy under the modified Tietz-Hua potential. However, the computation of the Shannon entropy and Information energy is an extension of the work of Falaye et al., who computed only the Fisher information under Tietz-Hua potential. [ABSTRACT FROM AUTHOR]

We propose two efficient entanglement concentration protocols (ECPs) for arbitrary less-entangled single-photon entanglement state, in which the photon qubit has the polarization feature. The first ECP is in linear optics, and the second ECP is in nonlinear optics. The two ECPs have some attractive advantages. First, they can preserve the polarization feature of the photon qubit, while all the other existing ECPs for single photon state cannot achieve this goal. Second, they only require one pair of less-entangled single-photon entanglement state and some auxiliary single photons. Third, they only require local operations. Especially, the second ECP can be used repeatedly, which can increase its success probability largely. Based on above properties, our two ECPs, especially the second one may be useful in current and future quantum communication.

Three-players Prisoners' dilemma (Alice, Bob and Colin) is studied in the presence of a single collective environment effect as a noise. The environmental effect is coupled with final states by a particular form of Kraus operators $$K_0$$ and $$K_1$$ through amplitude damping channel. We introduce the decoherence parameter $$0\le p\le 1$$ to the corresponding noise matrices, in order to controling the rate of environment influence on payoff of each players. Also, we consider the Unruh effect on the payoff of player, who is located at a noninertial frame. We suppose that two players (Bob and Colin) are in Rindler region I from Minkowski space-time, and move with same uniform acceleration ( $$r_b=r_c$$ ) and frequency mode. The game is begun with the classical strategies cooperation ( C) and defection ( D) accessible to each player. Furthermore, the players are allowed to access the quantum strategic space ( Q and M). The quantum entanglement is coupled with initial classical states by the parameter $$\gamma \in [0,\pi /2]$$ . Using entangled initial states by exerting an unitary operator $$\hat{J}$$ as entangling gate, the quantum game (competition between Prisoners, as a three-qubit system) is started by choosing the strategies from classical or quantum strategic space. Arbitrarily chosen strategy by each player can lead to achieving profiles, which can be considered as Nash equilibrium or Pareto optimal. It is shown that in the presence of noise effect, choosing quantum strategy Q results in a winning payoff against the classical strategy D and, for example, the strategy profile ( Q, D, C) is Pareto optimal. We find that the unfair miracle move of Eisert from quantum strategic space is an effective strategy for accelerated players in decoherence mode ( $$p=1$$ ) of the game. [ABSTRACT FROM AUTHOR]

In quantum information processing, rapid control is a basic requirement for performance improvement because a realistic quantum system cannot be perfectly separated from its environment, which will cause relaxation or decoherence effect. Rapid control may make the control law more robust to uncertainties in the model or in the control process. From the time optimization standpoint, bang-bang control is an excellent method for engineering practice. However, quantum bang-bang control relies on quantum Zeno effect, quantum anti-Zeno effect will occur under low measurement frequency, which intensifies the decoherence and leads to high-frequency oscillation phenomenon. In order to realize rapid state transfer and avoid high-frequency oscillation with an infinitesimal period in bang-bang Lyapunov control, we design control fields to realize arbitrary state transfer for non-Markovian system with phase relaxation and energy dissipative relaxation by Lyapunov stability theory. The numerical simulations illustrate that arbitrary state (eigenstate, superposition state or mixed state) transfer and maintenance for non-Markovian system can be realized under the approximate bang-bang Lyapunov control. [ABSTRACT FROM AUTHOR]

We study the absorption and dispersion properties of the three levels A -type superconducting quantum circuit driven by a pump field and a relatively weak probe field being applied to the different transitions. We find that the decoherence time between levels is critical to the observation of electromagnetically induced transparency (EIT) in superconducting quantum circuit. When the total decoherence time is fixed, it is necessary to ensure better coherence between levels |3⟩ ↔ |2⟩ than |3⟩ ↔ |1⟩ so as to exhibit obvious EIT. Furthermore, under given probe field, the bigger the Rabi frequency of probe field is, the wider the window of EIT, the easier to observe the transparency window. At this moment, however, slow light is inconspicuous and not conductive to optical information memory. [ABSTRACT FROM AUTHOR]

In this study, we investigate pairwise non-classical correlations measured using a one-way quantum deficit as well as quantum coherence in the XY spin-1/2 chain in a transverse magnetic field for both zero and finite temperatures. The analytical and numerical results of our investigations are presented. In the case when the temperature is zero, it is shown that the one-way quantum deficit can characterize quantum phase transitions as well as quantum coherence. We find that these measures have a clear critical point at λ = 1. When λ ≤ 1, the one-way quantum deficit has an analytical expression that coincides with the relative entropy of coherence. We also study an XX model and an Ising chain at the finite temperatures. [ABSTRACT FROM AUTHOR]

The entanglement evolution of a mixed three-qubit W-type state in three independent non-Markovian reservoirs with Lorentzian spectral density is investigated. The effects of the non-Markovianity of environment, initial state and the detuning on the entanglement dynamics in three-qubit system are presented. The results show that the entanglement between qubits in many-body system is more complicated than that in two-body system. First, the disentanglement criterion for two qubits is not suitable for multi qubits. Second, in many-body system, the effects of weight number characterizing the initial state distribution on the entanglement between two arbitrary qubits may be opposite. Further numerical calculations show that increasing the amount of non-Markovianity λ / γ , the purity of the initial quantum state or the detuning are all conducive to maintain the entanglement between qubits. [ABSTRACT FROM AUTHOR]

By virtue of the integration technique within ordered product of operators and Dirac’s representation theory we find a new formula for normally ordering coordinate-operator functions, that is f ( Q ˆ ) = : exp ( 1 4 ∂ 2 ∂ Q ˆ 2 ) f ( Q ˆ ) : , where Q ˆ is the coordinate operator, the symbol : : denotes normal ordering. Using this formula we can arrange a given quantum operator function f ( Q ˆ ) in its normal ordering conveniently and fast. Furthermore, we can derive a series of new relations about Hermite polynomial and Laguerre polynomial, as well as some new differential relations. [ABSTRACT FROM AUTHOR]