Controlled transfer of quantum amplitude via modulation of a potential barrier: numerical study in a model of SQUID

Coupling carbon nanotube mechanics to a superconducting circuit

The quantum behaviour of mechanical resonators is a new and emerging field driven by recent experiments reaching the quantum ground state. The high frequency, small mass, and large quality-factor of carbon nanotube resonators make them attractive for quantum nanomechanical applications. A common element in experiments achieving the resonator ground state is a second quantum system, such as coherent photons or superconducting device, coupled to the resonators motion. For nanotubes, however, this is a challenge due to their small size. Here, we couple a carbon nanoelectromechanical (NEMS) device…

Nondegenerate parametric oscillations in a tunable superconducting resonator

We investigate nondegenerate parametric oscillations in a multimode superconducting microwave resonator that is terminated by a SQUID. The parametric effect is achieved by modulating magnetic flux through the SQUID at a frequency close to the sum of two resonator-mode frequencies. For modulation amplitudes exceeding an instability threshold, self-sustained oscillations are observed in both modes. The amplitudes of these oscillations show good quantitative agreement with a theoretical model. The oscillation phases are found to be correlated and exhibit strong fluctuations which broaden the osci…

量子隧穿、全局相位与经典作用重构的极限

Quantum tunneling, global phases and the limits of classical action reconstructions

本文研究了经典作用重构在量子隧穿和相位现象中的局限性，指出需非零量子势或复作用来描述禁戒区，且全局边界条件对传输至关重要，同时指出Berry相位等现象存在全局相位约束。

激光诱导的石墨烯导电性调制与磁屏障

Laser-induced modulation of conductance in graphene with magnetic barriers

本研究通过激光与磁屏障的结合，实现了石墨烯电子传输的调制，利用Floquet理论和转移矩阵方法，发现激光能重塑电子相互作用，产生Fano共振和角度依赖的传输零点，实现可调谐的共振和完美传输。

Measuring the time a tunnelling atom spends in the barrier

Tunnelling is one of the most paradigmatic and evocative phenomena of quantum physics, underlying processes such as photosynthesis and nuclear fusion, as well as devices ranging from SQUID magnetometers to superconducting qubits for quantum computers. The question of how long a particle takes to tunnel, however, has remained controversial since the first attempts to calculate it, which relied on the group delay. It is now well understood that this delay (the arrival time of the transmitted wave packet peak at the far side of the barrier) can be smaller than the barrier thickness divided by the…

有限带宽储层中时间相关势垒电子输运的隧穿动力学与时间延迟

Tunneling Dynamics and Time Delay in Electron Transport through Time-Dependent Barriers with Finite-Bandwidth Reservoirs

通过绝热近似推导时间相关势垒的隧穿电流表达式，揭示势垒调制与稳态周期电流时间延迟的关系，并定义本征隧穿时间，发现宽/高势垒下隧穿时间消失，且时间延迟反映隧穿动力学的内禀性质。

Current resonances in graphene with time dependent potential barriers

A method is derived to solve the massless Dirac-Weyl equation describing electron transport in a mono-layer of graphene with a scalar potential barrier U(x,t), homogeneous in the y-direction, of arbitrary x- and time dependence. Resonant enhancement of both electron backscattering and currents, across and along the barrier, is predicted when the modulation frequencies satisfy certain resonance conditions. These conditions resemble those for Shapiro-steps of driven Josephson junctions. Surprisingly, we find a non-zero y-component of the current for carriers of zero momentum along the y-axis.

Space-time resolved quantum field approach to Klein tunneling dynamics across a finite barrier

We investigate Klein tunneling through finite potential barriers with space-time resolved solutions to relativistic quantum field equations. We find that no particle actually tunnels through a finite supercritical barrier, even in the case of resonant tunneling. The transmission is instead mediated by modulations in pair production rates, at each edge of the barrier, caused by the incoming electron. We further examine the effect of the barrier's width on the numbers of produced pairs in the fermionic case (characterized by saturation) and in the bosonic case (characterized by exponential super…

Rogue wavefunctions due to noisy quantum tunneling potentials

In this paper we study the effects of white-noised potentials on nonlinear quantum tunneling. We use a split-step scheme to numerically solve the nonlinear Schrodinger equation (NLSE) with a tunneling potential. We consider three different types of potentials, namely; the single rectangular barrier, double rectangular barrier and triangular barrier. For all these three cases we show that white-noise given to potentials do not trigger modulation instability for tunneling of the sech type soliton solutions of the NLSE. However white-noised potentials trigger modulation instability for tunneling …

双环超固态系统中的约瑟夫森涡旋和持续电流

Josephson vortices and persistent current in a double-ring supersolid system

研究径向耦合同心环状势阱中超冷偶极原子的超流-超固态相变，揭示旋转诱导的密度调制、持续电流以及中心涡旋和约瑟夫森涡旋的成核机制，并通过膨胀干涉图样区分不同涡旋构型。

dc to ac Josephson transition in a dc atom superconducting quantum interference device

We analyze the effect of the barrier motion on the Bose-Hubbard Hamiltonian of a ring-shaped Bose-Einstein condensate interrupted by a pair of Josephson junctions, a configuration which is the cold atom analog of the well-known dc superconducting quantum interference device (SQUID). Such an effect is also shown to modify the Heisenberg equation of motion of the boson field operator in the two-mode approximation, where a hysteretic contribution that could affect the dynamics for accelerated or overlapping barriers is identified. By studying the energy landscape as a function of order and contro…