We propose and study an approach to realize quantum switch for single-photon transport in a coupled superconducting transmission-line-resonator ͑TLR͒ array with one controllable hopping interaction. We find that the single photon with arbitrary wave vector can transport in a controllable way in this system. We also study how to realize controllable hopping interaction between two TLRs via a Cooper-pair box ͑CPB͒. When the frequency of the CPB is largely detuned from those of the two TLRs, the variables of the CPB can be adiabatically eliminated and thus a controllable interaction between two TLRs can be obtained.Coupled cavity arrays ͑CCAs͒ ͓1͔ have recently attracted considerable attentions of both theorists and experimentalists. The CCAs have been proposed to implement quantum simulators for many-body physics, such as discovering new matter phases of photons ͓2-4͔ and providing a new platform to study spin systems ͓5,6͔. The CCAs are also suggested to manipulate photons for optical quantum information processing ͓7-9͔. Moreover, photon transport in the CCAs has been investigated ͓10-14͔. There are several possible ways to construct the CCAs, for example: ͑i͒ coupled defect cavities in photonic crystals ͓15͔; ͑ii͒ coupled toroidal microresonators ͓16͔; and ͑iii͒ coupled superconducting transmission-line resonators ͑TLRs͒ ͓11,12͔.In CCAs, there have been many proposals to realize quantum switch ͓17,18͔, which is used to control single-photon transport ͓11,19-21͔. For example, the reflection and transmission of photons in a coupled resonator waveguide can be controlled by a tunable two-level quantum system ͓11,18͔, acting as a controller.Here, we study another approach to control the singlephoton transport in a CCA, which consists of a chain of TLRs ͓22,23͔. In our proposal, the controllable transport is realized by a tunable coupling. As we know, how to control coupling between two solid devices is a major challenge in scalable quantum computing circuits ͓24-30͔. To obtain a tunable coupling, we propose that a Cooper-pair box ͑CPB͒ acts as a coupler. When the frequency of the coupler is largely detuned from those of the two resonators, the variables of the coupler can be adiabatically eliminated and thus a controllable interaction can be induced. Compared with previous approach ͓11͔, this approach has following advantage: dynamical variables of the coupler are adiabatically eliminated, therefore the coupler is a passive controlling element, which makes robust to prevent from the environment of the coupler.As shown in Fig. 1, one-dimensional CCA is a chain of N cavities, each is only coupled to its nearest-neighbor ones, Figs. 1͑a͒ and 1͑b͒ are the site lattice model and the schematic of coupled TLR array, respectively. The TLRs are assumed to have the same frequency. We also assume that the coupling strength between two nearest-neighbor TLRs is the same, except one between the lth and ͑l +1͒th TLRs. The Hamiltonian of the system is H = ͚ n a n † a n − t ͚ n ͑a n † a n+1 + a n+1 † a n ͒ − t͑a l † a l+1 + a l+1 † a...

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We study the transverse-size effect of a quasi-one-dimensional rectangular waveguide on the single-photon scattering on a two-level system. We calculate the transmission and reflection coefficients for single incident photons using the scattering formalism based on the Lippmann-Schwinger equation. When the transverse size of the waveguide is larger than a critical size, we find that the transverse mode will be involved in the single-photon scattering. Including the coupling to a higher traverse mode, we find that the photon in the lowest channel will be lost into the other channel, corresponding to the other transverse modes, when the input energy is larger than the maximum bound-state energy. Three kinds of resonance phenomena are predicted: single-photon resonance, photonic Feshbach resonance, and cutoff (minimum) frequency resonance. At these resonances, the input photon is completely reflected.

The cellular irradiation-cross-linked polypropylene films treated by a hot-press process are corona charged to be piezoelectric. For the samples charged at room temperature, quasistatic piezoelectric d33 coefficients up to 400pC∕N are obtained. The d33 coefficients are slightly dependent on pressure in the range up to 50kPa. The d33 values decrease to 30% when the samples are exposed to 90°C for 1day; a preaging treatment improves the thermal stability of d33. The dominant drift path of the detrapped charges is from one void surface to the adjacent void surface through the bulk of the solid.

We study the photon blockade of two-photon scattering in a one-dimensional waveguide, which contains two atoms coupled via the Rydberg interaction. We obtain the analytic scattering solution of photonic wave packets with the Laplace transform method. We examine the photon correlation by addressing the two-photon relative wave function and the second-order correlation function in the single- and two-photon resonance cases. It is found that, under the single-photon resonance condition, photon bunching and antibunching can be observed in the two-photon transmission and reflection, respectively. In particular, the bunching and antibunching effects become stronger with the increasing of the Rydberg coupling strength. In addition, we find a phenomenon of bunching-antibunching transition caused by the two-photon resonance.Comment: 9 pages, 4 figure

We study coherent energy transfer of a single excitation and quantum entanglement in a dimer, which consists of a donor and an acceptor modeled by two two-level systems. Between the donor and the acceptor, there exists a dipole-dipole interaction, which provides the physical mechanism for coherent energy transfer and entanglement generation. The donor and the acceptor couple to two independent heat baths with diagonal couplings that do not dissipate the energy of the non-coupling dimer. Special attention is paid to the effect on single-excitation energy transfer and entanglement generation of the energy detuning between the donor and the acceptor and the temperatures of the two heat baths. It is found that, the probability for single-excitation energy transfer largely depends on the energy detuning in the low temperature limit. Concretely, the positive and negative energy detunings can increase and decrease the probability at the steady state, respectively. In the high temperature limit, however, the effect of the energy detuning on the probability is neglectably small. We also find that the probability is neglectably dependent on the bath temperature difference of the two heat baths. In addition, it is found that quantum entanglement can be generated in the process of coherent energy transfer. As the bath temperature increases, the generated steady state entanglement decreases. For a given bath temperature, the steady-state entanglement decreases with the increasing of the absolute value of the energy detuning.Comment: 13 pages, 11 figure

We study analytically the quantum thermalization of two coupled two-level systems (TLSs), which are connected with either two independent heat baths (IHBs) or a common heat bath (CHB). We understand the quantum thermalization in eigenstate and bare-state representations when the coupling between the two TLSs is stronger and weaker than the TLS-bath couplings, respectively. In the IHB case, we find that when the two IHBs have the same temperatures, the two coupled TLSs in eigenstate representation can be thermalized with the same temperature as those of the IHBs. However, in the case of two IHBs at different temperatures, just when the energy detuning between the two TLSs satisfies a special condition, the two coupled TLSs in eigenstate representation can be thermalized with an immediate temperature between those of the two IHBs. In bare-state representation, we find a counterintuitive phenomenon that, under some conditions, the temperature of the TLS connected with the high-temperature bath is lower than that of the other TLS, which is connected with the low-temperature bath. In the CHB case, the coupled TLSs in eigenstate representation can be thermalized with the same temperature as that of the CHB in nonresonant cases. In bare-state representation, the TLS with a larger energy separation can be thermalized to a thermal equilibrium with a lower temperature. In the resonant case, we find a phenomenon of anti-thermalization. We also study the steady-state entanglement between the two TLSs in both the IHB and CHB cases.

We propose a scheme to generate macroscopic Schrödinger-cat states in a quantum harmonic oscillator (electromagnetic field or mechanical resonator) coupled to a quantum bit (two-level system) via a conditional displacement mechanism. By driving the qubit monochromatically, the oscillation of the qubit state modifies the effective frequency of the driving force acting on the oscillator, and a resonant or near-resonant driving on the oscillator can be achieved. The displacement of the oscillator is then significantly enhanced due to the small detuning of the driving force and can exceed that of the zero-point fluctuation. This effect can be used to prepare quantum superpositions of macroscopically distinct coherent states in the oscillator. We present detailed studies on this state-generation scheme in both the closed-and open-system cases. This approach can be implemented in various experimental platforms, such as cavity-or circuit-QED systems, electromechanical systems, and spin-cantilever systems.