39 research outputs found
Many-body synchronization of interacting qubits by engineered ac-driving
In this work we introduce the many-body synchronization of an interacting
qubit ensemble which allows one to switch dynamically from many-body-localized
(MBL) to an ergodic state. We show that applying of -pulses with altering
phases, one can effectively suppress the MBL phase and, hence, eliminate qubits
disorder. The findings are based on the analysis of the Loschmidt echo dynamics
which shows a transition from a power-law decay to more rapid one indicating
the dynamical MBL-to-ergodic transition. The technique does not require to know
the microscopic details of the disorder.Comment: 5 pages, 4 figure
Dispersive Response of a Disordered Superconducting Quantum Metamaterial
We consider a disordered quantum metamaterial formed by an array of
superconducting flux qubits coupled to microwave photons in a cavity. We map
the system on the Tavis-Cummings model accounting for the disorder in
frequencies of the qubits. The complex transmittance is calculated with the
parameters taken from state-of-the-art experiments. We demonstrate that photon
phase shift measurements allow to distinguish individual resonances in the
metamaterial with up to 100 qubits, in spite of the decoherence spectral width
being remarkably larger than the effective coupling constant. Our simulations
are in agreement with the results of the recently reported experiment.Comment: 10 pages, 4 figure
Coulomb blockade of chiral Majorana and complex fermions far from equilibrium
We study charge transport in a single-electron transistor implemented as an
interferometer such that the Coulomb blockaded middle island contains a
circular chiral Majorana or Dirac edge mode. We concentrate on the regime of
small conductance and provide an asymptotic solution in the limit of high
transport voltage exceeding the charging energy. The solution is achieved using
an instanton-like technique. The distinctions between Majorana and Dirac cases
appears when the tunnel junctions are unequal. The main difference is in the
offset current at high voltages which can be higher up to in Majorana
case. It is caused by an additional particle-hole symmetry of the distribution
function in the Majorana case. There is also an eye-catching distinction
between the oscillations patterns of the current as a function of the gate
charge. We conjecture this distinction survives at lower transport voltages as
well.Comment: 11 pages, 5 figure
Cavity-QED simulation of a quantum metamaterial with tunable disorder
We explore experimentally a quantum metamaterial based on a superconducting chip with 25 frequency-tunable transmon qubits coupled to a common coplanar resonator. The collective bright and dark modes are probed via the microwave response, i.e., by measuring the transmission amplitude of an external microwave signal. All qubits have individual control and readout lines. Their frequency tunability allows to change the number N of resonantly coupled qubits and also to introduce a disorder in their excitation frequencies with preassigned distributions. While increasing N, we demonstrate the expected N scaling law for the energy gap (Rabi splitting) between bright modes around the cavity frequency. By introducing a controllable disorder and averaging the transmission amplitude over a large number of realizations, we demonstrate a decay of mesoscopic fluctuations which mimics an approach towards the thermodynamic limit. The collective bright states survive in the presence of disorder when the strength of individual qubit coupling to the cavity dominates over the disorder strength