40 research outputs found
Scalable Ion Trap Architecture for Universal Quantum Computation by Collisions
We propose a scalable ion trap architecture for universal quantum
computation, which is composed of an array of ion traps with one ion confined
in each trap. The neighboring traps are designed capable of merging into one
single trap. The universal two-qubit gate is realized by direct
collision of two neighboring ions in the merged trap, which induces an
effective spin-spin interaction between two ions. We find that the
collision-induced spin-spin interaction decreases with the third power of two
ions' trapping distance. Even with a trapping distance between
atomic ions in Paul traps, it is still possible to realize a two-qubit gate
operation with speed in regime. The speed can be further increased
up into regime using electrons with trapping distance in
Penning traps.Comment: 5 pages, 1 figur
Quantum Dynamics of Mesoscopic Driven Duffing Oscillators
We investigate the nonlinear dynamics of a mesoscopic driven Duffing
oscillator in a quantum regime. In terms of Wigner function, we identify the
nature of state near the bifurcation point, and analyze the transient process
which reveals two distinct stages of quenching and escape. The rate process in
the escape stage allows us to extract the transition rate, which displays
perfect scaling behavior with the driving distance to the bifurcation point. We
numerically determine the scaling exponent, compare it with existing result,
and propose open questions to be resolved.Comment: 4 pages, 4 figures; revised version accepted for publication in EP
Condensed Matter Physics in Time Crystals
Time crystals are physical systems whose time translation symmetry is
spontaneously broken. Although the spontaneous breaking of continuous
time-translation symmetry in static systems is proved impossible for the
equilibrium state, the discrete time-translation symmetry in periodically
driven (Floquet) systems is allowed to be spontaneously broken, resulting in
the so-called Floquet or discrete time crystals. While most works so far
searching for time crystals focus on the symmetry breaking process and the
possible stabilising mechanisms, the many-body physics from the interplay of
symmetry-broken states, which we call the condensed matter physics in time
crystals, is not fully explored yet. This review aims to summarise the very
preliminary results in this new research field with an analogous structure of
condensed matter theory in solids. The whole theory is built on a hidden
symmetry in time crystals, i.e., the phase space lattice symmetry, which allows
us to develop the band theory, topology and strongly correlated models in phase
space lattice. In the end, we outline the possible topics and directions for
the future research.Comment: Review article, 30+9 pages, 12 figures; more references added in the
2nd versio
Emission spectrum of the driven nonlinear oscillator
Motivated by recent "circuit QED" experiments we investigate the noise
properties of coherently driven nonlinear resonators. By using Josephson
junctions in superconducting circuits, strong nonlinearities can be engineered,
which lead to the appearance of pronounced effects already for a low number of
photons in the resonator. Based on a master equation approach we determine the
emission spectrum and observe for typical circuit QED parameters, in addition
to the primary Raman-type peaks, second-order peaks. These peaks describe
higher harmonics in the slow noise-induced fluctuations of the oscillation
amplitude of the resonator and provide a clear signature of the nonlinear
nature of the system.Comment: 8 pages, 5 figure
The giant acoustic atom --- a single quantum system with a deterministic time delay
We investigate the quantum dynamics of a single transmon qubit coupled to
surface acoustic waves (SAWs) via two distant connection points. Since the
acoustic speed is five orders of magnitude slower than the speed of light, the
travelling time between the two connection points needs to be taken into
account. Therefore, we treat the transmon qubit as a giant atom with a
deterministic time delay. We find that the spontaneous emission of the system,
formed by the giant atom and the SAWs between its connection points, initially
decays polynomially in the form of pulses instead of a continuous exponential
decay behaviour, as would be the case for a small atom. We obtain exact
analytical results for the scattering properties of the giant atom up to
two-phonon processes by using a diagrammatic approach. We find that two peaks
appear in the inelastic (incoherent) power spectrum of the giant atom, a
phenomenon which does not exist for a small atom. The time delay also gives
rise to novel features in the reflectance, transmittance, and second-order
correlation functions of the system. Furthermore, we find the short-time
dynamics of the giant atom for arbitrary drive strength by a numerically exact
method for open quantum systems with a finite-time-delay feedback loop.Comment: To be published on Physical Review