43 research outputs found
Nonclassical Radiation from Thermal Cavities in the Ultrastrong Coupling Regime
Thermal or chaotic light sources emit radiation characterized by a slightly
enhanced probability of emitting photons in bunches, described by a zero-delay
second-order correlation function . Here we explore
photon-coincidence counting statistics of thermal cavities in the ultrastrong
coupling regime, where the atom-cavity coupling rate becomes comparable to the
cavity resonance frequency. We find that, depending on the system temperature
and coupling rate, thermal photons escaping the cavity can display very
different statistical behaviors, characterised by second-order correlation
functions approaching zero or greatly exceeding two.Comment: results on frequency resolved photon correlations added, to appear in
Phys. Rev. Let
Photon correlations from ultra-strong optical nonlinearities
We study the full field and frequency filtered output photon statistics of a
resonator in thermal equilibrium with a bath and containing an arbitrarily
large quartic nonlinearity. According to the general theory of photodetection,
we derive general input-output relations valid for the ultra-anharmonic regime,
where the nonlinearity becomes comparable to the energy of the resonator, and
show how the emission properties are modified as compared to the generally
assumed simple anharmonic regime. We analyse the impact of the nonlinearity on
the full statistics of the emission and its spectral properties. In particular
we derive a semi-analytical expression for the frequency resolved two-photon
correlations or two-photon spectrum of the system in terms of the master
equation coefficients and density matrix. This provides a very clear insight
into the level structure and emission possibilities of the system.Comment: 10 pages, 7 figure
All Optical Switch of Vacuum Rabi Oscillations: The Ultrafast Quantum Eraser
We study the all-optical time-control of the strong coupling between a single
cascade three-level quantum emitter and a microcavity. We find that only
specific arrival-times of the control pulses succeed in switching-off the Rabi
oscillations. Depending on the arrival times of control pulses, a variety of
exotic non-adiabatic cavity quantum electrodynamics effects can be observed. We
show that only control pulses with specific arrival times are able to suddenly
switch-off and -on first-order coherence of cavity photons, without affecting
their strong coupling population dynamics. Such behavior may be understood as a
manifestation of quantum complementarity
Photodetection probability in quantum systems with arbitrarily strong light-matter interaction
Cavity-QED systems have recently reached a regime where the light-matter
interaction strength amounts to a non-negligible fraction of the resonance
frequencies of the bare subsystems. In this regime, it is known that the usual
normal-order correlation functions for the cavity-photon operators fail to
describe both the rate and the statistics of emitted photons. Following
Glauber's original approach, we derive a simple and general quantum theory of
photodetection, valid for arbitrary light-matter interaction strengths. Our
derivation uses Fermi's golden rule, together with an expansion of system
operators in the eigenbasis of the interacting light-matter system, to arrive
at the correct photodetection probabilities. We consider both narrow- and
wide-band photodetectors. Our description is also valid for point-like
detectors placed inside the optical cavity. As an application, we propose a
gedanken experiment confirming the virtual nature of the bare excitations that
enrich the ground state of the quantum Rabi model.Comment: 9 pages, 1 figur
Non-perturbative Dynamical Casimir Effect in Optomechanical Systems: Vacuum Casimir-Rabi Splittings
We study the dynamical Casimir effect using a fully quantum-mechanical
description of both the cavity field and the oscillating mirror. We do not
linearize the dynamics, nor do we adopt any parametric or perturbative
approximation. By numerically diagonalizing the full optomechanical
Hamiltonian, we show that the resonant generation of photons from the vacuum is
determined by a ladder of mirror-field {\em vacuum Rabi splittings}. We find
that vacuum emission can originate from the free evolution of an initial pure
mechanical excited state, in analogy with the spontaneous emission from excited
atoms. By considering a coherent drive of the mirror, using a master-equation
approach to take losses into account, we are able to study the dynamical
Casimir effect for optomechanical coupling strengths ranging from weak to
ultrastrong. We find that a resonant production of photons out of the vacuum
can be observed even for mechanical frequencies lower than the cavity-mode
frequency. Since high mechanical frequencies, which are hard to achieve
experimentally, were thought to be imperative for realizing the dynamical
Casimir effect, this result removes one of the major obstacles for the
observation of this long-sought effect. We also find that the dynamical Casimir
effect can create entanglement between the oscillating mirror and the radiation
produced by its motion in the vacuum field, and that vacuum Casimir-Rabi
oscillations can occur.Comment: 30 pages, 8 figure
Revealing higher-order light and matter energy exchanges using quantum trajectories in ultrastrong coupling
The dynamics of open quantum systems is often modeled using master equations, which describe the expected outcome of an experiment (i.e., the average over many realizations of the same dynamics). Quantum trajectories, instead, model the outcome of ideal single experiments - the "clicks"of a perfect detector due to, e.g., spontaneous emission. The correct description of quantum jumps, which are related to random events characterizing a sudden change in the wave function of an open quantum system, is pivotal to the definition of quantum trajectories. In this article, we extend the formalism of quantum trajectories to open quantum systems with ultrastrong coupling (USC) between light and matter by properly defining jump operators in this regime. In such systems, exotic higher-order quantum-state and energy transfer can take place without conserving the total number of excitations in the system. The emitted field of such USC systems bears signatures of these higher-order processes, and significantly differs from similar processes at lower coupling strengths. Notably, the emission statistics must be taken at a single quantum trajectory level, since the signatures of these processes are washed out by the "averaging"of a master equation. We analyze the impact of the chosen unraveling (i.e., how one collects the output field of the system) for the quantum trajectories and show that these effects of the higher-order USC processes can be revealed in experiments by constructing histograms of detected quantum jumps. We illustrate these ideas by analyzing the excitation of two atoms by a single photon [Garziano, Phys. Rev. Lett. 117, 043601 (2016)0031-900710.1103/PhysRevLett.117.043601]. For example, quantum trajectories reveal that keeping track of the quantum jumps from the atoms allows one to reconstruct both the oscillations between one photon and two atoms as well as emerging Rabi oscillations between the two atoms
Dissipation and Thermal Noise in Hybrid Quantum Systems in the Ultrastrong Coupling Regime
The interaction among the components of a hybrid quantum system is often
neglected when considering the coupling of these components to an environment.
However, if the interaction strength is large, this approximation leads to
unphysical predictions, as has been shown for cavity-QED and optomechanical
systems in the ultrastrong-coupling regime. To deal with these cases, master
equations with dissipators retaining the interaction between these components
have been derived for the quantum Rabi model and for the standard
optomechanical Hamiltonian. In this article, we go beyond these previous
derivations and present a general master equation approach for arbitrary hybrid
quantum systems interacting with thermal reservoirs. Specifically, our approach
can be applied to describe the dynamics of open hybrid systems with harmonic,
quasi-harmonic, and anharmonic transitions. We apply our approach to study the
influence of temperature on multiphoton vacuum Rabi oscillations in circuit
QED. We also analyze the influence of temperature on the conversion of
mechanical energy into photon pairs in an optomechanical system, which has been
recently described at zero temperature. We compare our results with previous
approaches, finding that these sometimes overestimate decoherence rates and
understimate excited-state populations