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Mechanical oscillators can be implemented to store and transfer information or to build hybrid systems. In order to couple a mechanical oscillator to a superconducting qubit, we fabricate a superconducting capacitor, in which diluted photoresist or electron beam photoresist is used as sacrificial layers. The upper plate of the capacitor, a suspended membrane, acts as a mechanical oscillator. We obtain its mechanical resonant frequency and response to the input microwave. Such mechanical oscillators can be used as the capacitor of a superconducting qubit to form a coupled system. In order to control the resonant frequency of the mechanical oscillator and the microwave resonator, we introduce a dc voltage bias between the upper and lower plates of the capacitor. We analyze the electromechanical coupling such as pull-in effect and experimentally demonstrate the dependence of the resonant frequency on the applied dc voltage. These results will contribute to the design and fabrication of hybrid systems comprising voltage-controlled mechanical oscillators and other systems.

Biological activated carbon (BAC) filtration is usually considered to be able to decrease formation potentials (FPs) of disinfection by-products (DBPs) in drinking water treatment plant (DWTP). However, BAC filters with long running time may release microbial metabolites to effluents and therefore increase FPs of nitrogenous DBPs with high toxicity. To verify this hypothesis, this study continuously tracked BAC filters in a DWTP for one year, and assessed effects of old (running time 8–9 years) and new (running time 0–13 months) BAC filters on FPs of 15 regulated and unregulated DBPs. Results revealed that dissolved organic carbon (DOC) removal was slightly higher in the new BAC than the old one. All fluorescent components of dissolved organic matter evidently declined after new BAC filtration, but fulvic acid-like and soluble microbial product-like substances increased after old BAC filtration, which could be caused by microbial leakage. Correspondingly, new BAC filter generally removed more DBP FPs than the old one. 46.5% HAA7 FPs from chlorination and 44.3% THM4 FPs from chloramination were removed by new BAC filter. However, some DBP FPs, especially HAN FPs, were poorly removed or even increased by the old BAC filter. Proteobacteria could be a main contributor for DBP precursor removal in BAC filters. Herminiimonas, most abundant genera in new BAC filter, may explain its better DOC and UV254 removal performance and lower DBP FPs, while Bradyrhizobium, most abundant genera in old BAC filter, might produce more extracellular polymeric substances and therefore increased N-DBP FPs in old BAC effluent. This study provided insight into variations of DBP FPs and microbial communities in the new and old BAC filters, and will be helpful for the optimization of DWTP design and operation for public health.

Biological activated carbon (BAC) filtration is an effective technology for the removal of natural organic matter. However, one potential drawback of BAC, especially old BAC, is that effluents can contain soluble microbial products released from the biofilm, which are recognized as more toxic nitrogenous DBPs (N-DBPs) precursors. So far, limited studies reported the risk of DBP formation potentials (FPs) increase caused by the microbial leakage of BAC. This study compared removal differences of DBP FPs between two BAC filters operated for 1 year and 8 years in a drinking water plant. The results showed that the total summed haloacetic acid FPs and trihalomethane FPs decreased by 34.31% from chlorination, and 55.01% of the total summed halogen acetonitrile FPs from chloramination were removed by the new BAC. However, Chlorinated haloacetonitriles FPs increased by 2.33% after old BAC filtration. To sum up, BAC filtration decreased most DBP FPs, but a potential risk regarding more toxic N-DBP FPs from old BAC should receive more attention.

We present a fishbone-like lumped-element artificial transmission line to overcome impedance mismatch in a reflection-type Josephson parametric amplifier between a nonlinear resonator and an external transmission line. Using this easily prepared architecture, we design and fabricate a broadband Josephson parametric amplifier, which has gain in an excess of 20 dB with a bandwidth of hundreds of MHz. Furthermore, by varying the working point of the device, the operating frequency of amplification can be tuned in a wide frequency range of 1 GHz while the amplifier operates in the mode of either three-wave mixing or four-wave mixing. Such a parametric amplifier is suitable for engineering applications of superconducting circuit quantum electrodynamics.

Mechanical oscillators can be implemented to store and/or transfer information. In order to couple a mechanical oscillator to a superconducting qubit, we fabricate a superconducting capacitor using the diluted photoresist or electron beam photoresist as a sacrificial layer. The upper plate of the capacitor, a suspended membrane, acts as a mechanical oscillator. We obtain its mechanical resonant frequency and response to the input microwave. Such mechanical oscillator can be used as the capacitor of a superconducting qubit to form a coupled system. Another way to transfer information between a mechanical oscillator and a superconducting qubit is to take advantage of a superconducting microwave resonator such as a coplanar waveguide resonator. In order to control the resonant frequency of the resonators, we introduce a DC voltage bias between the upper and lower plates of the capacitor. We demonstrate the dependence of the resonant frequency on the applied DC voltage.

We fabricate a microscale electromechanical system, in which a suspended superconducting membrane, treated as a mechanical oscillator, capacitively couples to a superconducting microwave resonator. As the microwave driving power increases, nonmonotonic dependence of the resonance frequency of the mechanical oscillator on the driving power has been observed. We also demonstrate the optical switching of the resonance frequency of the mechanical oscillator. Theoretical models for qualitative understanding of our experimental observations are presented. Our experiment may pave the way for the application of a mechanical oscillator with its resonance frequency controlled by the electromagnetic and/or optical fields, such as a microwave-optical interface and a controllable element in a superqubit-mechanical oscillator hybrid system., 8 pages,4 figures

An impedance matched parametric amplifier (IMPA) with Josephson junctions is fabricated and characterized. A hybrid structure containing coplanar and strip structures is implemented to realize an impedance taper line and a plate capacitor in an LC nonlinear resonator based on Josephson junctions. The upper plate of the capacitor is isolated with SiN x without grounding as well as the strips. Such easily-prepared designs greatly reduce the requirements for lithography alignment and precision, which makes the fabrication process more reliable. The experimental results show that in such IMPA a gain higher than 25 dB with a bandwidth of about 100 MHz can be obtained. This broadband amplifier operates close to the quantum limit. By adjusting the working point, a higher bandwidth of about 400 MHz can be obtained with a gain of about 17 dB.

We design and fabricate λ/2 coplanar waveguide NbN resonators, the thickness and length of which are only several nanometers and hundred microns, respectively. The quality factor of such compact resonators can reach up to 7.5 × 104 at single photon power level at 30 mK with the resonance frequency around 6.835 GHz. In order to tune the resonant frequency, the resonator is terminated to the ground with a dc-SQUID. By tuning the magnetic flux in the dc-SQUID, the effective inductance of the dc-SQUID is varied, which leads to the change in the resonant frequency of the resonator. The tunability range is more than 30 MHz and the quality factor is about 3 × 103. These compact and tunable NbN resonators have potential applications in the quantum information processing, such as in the precision measurement, coupling and/or reading out the quantum states of qubits.

We propose a versatile scheme for multiphoton frequency up/down conversion in flux superconducting qubit circuits, driven by a pair of microwaves tuned near and far off the qubit resonance. Flux qubits can be engineered with strong anharmonicity such that the two lowest eigenstates are energetically well separated from the higher ones. We demonstrate the high order non-linear transitions between the two lowest levels in the three-photon regime, by coupling the qubit to bichromatic microwave fields with the same Rabi frequencies. Both up and down conversions are presented, and accurately interpreted with many-mode Floquet formalism. An intuitive graph theoretic approach elucidates the physics of multiphoton pumping and population trapping. The analytical solutions also illustrate how controllability is achievable for desired single- or multiphoton pumping processes in a wide range of frequencies. The proposed design and theoretical approach are applicable in maintaining the inter-connectivity of future superconducting quantum machines.

By adjusting the frequency of the cavity, we perform a microwave reflection measurement and directly probe the coherence and interference effects in a phase-sensitive Josephson parametric amplifier. We demonstrate the shift in the peak and the dip in the reflection spectra of the amplifier, which operates in the phase-sensitive mode. The behavior of the shift can be precisely controlled by tuning the pump power, the frequency of the cavity, and the relative phase between the incident signal and pump field. Theoretical simulations are in good agreement with the experimental results. These results provide an alternative way of controlling the parametric process by adjusting the frequency of the cavity.

In order to obtain high-quality superconducting qubits, we employed a cold-development technique, using temperatures down to −20°C, to fabricate Al/AlO x /Al Josephson junctions. Cold development greatly reduced the sensitivity of the electron-beam resist to the developer, eliminated molecules of the electron-beam resist at trench edges, and improved the repeatability and reliability of the nanopatterning process. The fabricated samples have well-defined geometries and increased dose margins, with lateral sizes of 100 nm×100 nm on both silicon and sapphire substrates. Together with the bridge-free fabrication method we used in these experiments, we believe that the cold-development technique can play an important role in quantum information technology that employs superconducting qubits.

We report experimental observation of two distinct quantum interference patterns in the absorption spectra when a transmon superconducting qubit is subjected to a bichromatic microwave field with the same Rabi frequencies. Within the two-mode Floquet formalism with no dissipation processes, we propose a graph-theoretical representation to model the interaction Hamiltonian for each of these observations. This theoretical framework provides a clear visual representation of various underlying physical processes in a systematic way beyond rotating-wave approximation. The presented approach is valuable to gain insights into the behavior of multichromatic field driven quantum two-level systems, such as two-level atoms and superconducting qubits. Each of the observed interference patterns is represented by appropriate graph products on the proposed color-weighted graphs. The underlying mechanisms and the characteristic features of the observed fine structures are identified by the transitions between the graph vertices, which represent the doubly dressed states of the system. The good agreement between the numerical simulation and experimental data confirms the validity of the theoretical method. Such multiphoton interference may be used in manipulating the quantum states and/or generate nonclassical microwave photons.

By applying a coupling microwave field gated by random-telegraph-noise (RTN), we report the experimental demonstration of dynamically modulated Autler-Townes effect (ATE) in an artificial atom---a superconducting transmon qubit---and obtain the distinguished characteristics when a system is affected by RTN. By further applying another coupling microwave filed on the transmon, we use an intense bichromatic field to couple the energy levels. Depending on the detuning of the couplers, remarkable interference patterns emerge in the spectrum, which come from the dressed states induced by the modulated ATE. Numerical calculations agree well with the experimental data.

By driving a 3D transmon with microwave fields, we generate an effective avoided energy-level crossing. Then we chirp microwave frequency, which is equivalent to driving the system through the avoided energy-level crossing by sweeping the avoided crossing. A double-passage chirp produces Landau-Zener-Stuckelberg-Majorana (LZSM) interference that agree well with the numerical results, especially with the initial state being an eigen-energy state in the center of an avoided level crossing. A time-resolved state tomography measurement is performed in the evolution of LZSM interference, showing an experimental evidence for the dynamical evolution of quantum state. Our method is fully applicable to other quantum systems that contain no intrinsic avoided level crossing, providing an alternative approach for quantum control and quantum simulation.

We propose a novel type of plasmonic lasing nanostructure consisting of a metallic shell and a gain core. We demonstrate numerically that highly localized void modes of such metallodielectric core-shell nanoparticles have a very high quality factor. We found that the dipole void mode has a lasing threshold as low as 128 cm(-1) at 800 nm as a result of the unique mode distribution within the shell, due to a maximum field enhancement around the void center. The lasing condition for a symmetry-reduced silver nanocup is also investigated and the low plasmonic lasing threshold is sustained provided that the opening angle of the nanocup is smaller than 10°. Our proposal presents a new path toward plasmonic lasers with low gain threshold.

We studied theoretically the diffraction coupling of magnetic resonances in metamaterials consisting of a planar rectangular array of metal rod pairs with a dielectric spacer. A narrow-band mixed mode was observed due to a strong interaction between magnetic resonances in individual pairs of metal rods and an in-plane propagating collective surface mode arising from the array periodicity. Upon the excitation of this mixed mode, a five-fold enhancement of magnetic field in the dielectric spacer was achieved as compared with the purely magnetic resonance. It was also found that only a collective surface mode with its magnetic field parallel to the array plane could mediate the excitation of such a mixed mode.

We have realized a frequency-tunable transmon in a three-dimensional cooper cavity using a direct current superconducting quantum interference device. Both the transition frequency of the transmon and the frequency of the dressed cavity can be varied with the applied external flux bias, which are well consistent with the theoretical model. The range of the variable transition frequency is from 5.188 GHz to 7.756 GHz. The energy relaxation time of the transmon is hundreds of nanoseconds.