71 research outputs found
Canonical circuit quantization with linear nonreciprocal devices
Nonreciprocal devices effectively mimic the breaking of time-reversal
symmetry for the subspace of dynamical variables that they couple, and can be
used to create chiral information processing networks. We study the systematic
inclusion of ideal gyrators and circulators into Lagrangian and Hamiltonian
descriptions of lumped-element electrical networks. The proposed theory is of
wide applicability in general nonreciprocal networks on the quantum regime. We
apply it to pedagogical and pathological examples of circuits containing
Josephson junctions and ideal nonreciprocal elements described by admittance
matrices, and compare it with the more involved treatment of circuits based on
nonreciprocal devices characterized by impedance or scattering matrices.
Finally, we discuss the dual quantization of circuits containing phase-slip
junctions and nonreciprocal devices.Comment: 12 pages, 4 figures; changes made to match the accepted version in
PR
Quantum Simulator for Transport Phenomena in Fluid Flows
Transport phenomena still stand as one of the most challenging problems in
computational physics. By exploiting the analogies between Dirac and lattice
Boltzmann equations, we develop a quantum simulator based on pseudospin-boson
quantum systems, which is suitable for encoding fluid dynamics transport
phenomena within a lattice kinetic formalism. It is shown that both the
streaming and collision processes of lattice Boltzmann dynamics can be
implemented with controlled quantum operations, using a heralded quantum
protocol to encode non-unitary scattering processes. The proposed simulator is
amenable to realization in controlled quantum platforms, such as ion-trap
quantum computers or circuit quantum electrodynamics processors.Comment: 8 pages, 3 figure
Transition from discrete to continuous time of arrival distribution for a quantum particle
We show that the Kijowski distribution for time of arrivals in the entire
real line is the limiting distribution of the time of arrival distribution in a
confining box as its length increases to infinity. The dynamics of the confined
time of arrival eigenfunctions is also numerically investigated and
demonstrated that the eigenfunctions evolve to have point supports at the
arrival point at their respective eigenvalues in the limit of arbitrarilly
large confining lengths, giving insight into the ideal physical content of the
Kijowsky distribution.Comment: Accepted for publication in Phys. Rev.
Sources of quantum waves
Due to the space and time dependence of the wave function in the time
dependent Schroedinger equation, different boundary conditions are possible.
The equation is usually solved as an ``initial value problem'', by fixing the
value of the wave function in all space at a given instant. We compare this
standard approach to "source boundary conditions'' that fix the wave at all
times in a given region, in particular at a point in one dimension. In contrast
to the well-known physical interpretation of the initial-value-problem
approach, the interpretation of the source approach has remained unclear, since
it introduces negative energy components, even for ``free motion'', and a
time-dependent norm. This work provides physical meaning to the source method
by finding the link with equivalent initial value problems.Comment: 12 pages, 7 inlined figures; typos correcte
The Coherence of Primordial Fluctuations Produced During Inflation
The behaviour of quantum metric perturbations produced during inflation is
considered at the stage after the second Hubble radius crossing. It is shown
that the classical correlation between amplitude and momentum of a perturbation
mode, previously shown to emerge in the course of an effective
quantum-to-classical transition, is maintained for a sufficiently long time,
and we present the explicit form in which it takes place using the Wigner
function. We further show with a simple diffraction experiment that quantum
interference, non-expressible in terms of a classical stochastic description of
the perturbations, is essentially suppressed. Rescattering of the perturbations
leads to a comparatively slow decay of this correlation and to a complete
stochastization of the system.Comment: LaTeX (7 pages
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