58 research outputs found
Non-Markovian Quantum Dynamics in Strongly Coupled Multimode Cavities Conditioned on Continuous Measurement
Estimation of the geometric measure of entanglement with Wehrl Moments through Artificial Neural Networks
In recent years, artificial neural networks (ANNs) have become an
increasingly popular tool for studying problems in quantum theory, and in
particular entanglement theory. In this work, we analyse to what extent ANNs
can accurately predict the geometric measure of entanglement of symmetric
multiqubit states using only a limited number of Wehrl moments (moments of the
Husimi function of the state) as input, which represents partial information
about the state. We consider both pure and mixed quantum states. We compare the
results we obtain by training ANNs with the informed use of convergence
acceleration methods. We find that even some of the most powerful convergence
acceleration algorithms do not compete with ANNs when given the same input
data, provided that enough data is available to train these ANNs. We also
provide an experimental protocol for measuring Wehrl moments, which is
state-independent. More generally, this work opens up perspectives for the
estimation of entanglement measures and other SU(2)-invariant quantities, such
as the Wehrl entropy, in a way that is more accessible in experiments than by
means of full state tomography.Comment: 27 pages, 14 figures v3: expanded manuscript with a new section on an
experimental protocol for measuring Wehrl moment
Spectral Theory of Non-Markovian Dissipative Phase Transitions
To date, dissipative phase transitions (DPTs) have mostly been studied for
quantum systems coupled to idealized Markovian (memoryless) environments, where
the closing of the Liouvillian gap constitutes a hallmark. Here, we extend the
spectral theory of DPTs to arbitrary non-Markovian systems and present a
general and systematic method to extract their signatures, which is fundamental
for the understanding of realistic materials and experiments such as in the
solid-state, cold atoms, cavity or circuit QED. We first illustrate our theory
to show how memory effects can be used as a resource to control phase
boundaries in a model exhibiting a first-order DPT, and then demonstrate the
power of the method by capturing all features of a challenging second-order DPT
in a two-mode Dicke model for which previous attempts had failed up to now.Comment: 7 pages and 3 figures (main), 12 pages and 6 figures (SM
Théorie spectrale des transitions de phase dissipatives non-markoviennes
So far, dissipative phase transitions (DPTs) have been mostly studied for quantum systems coupled to idealized Markovian (memoryless) environments, where the closing of the Liouvillian gap consitutes a hallmark.
Here, we extend the spectral theory of DPTs to arbitrary non-Markovian systems and present a general and systematic numerical method to extract their signatures, which is fundamental for the understanding of realistic materials and experimental platforms such as in the solid-state, cold atoms, or cavity and circuit QED
Master equation for collective spontaneous emission with quantized atomic motion
We derive a markovian master equation for the internal dynamics of an ensemble of two-level atoms including the quantization of their motion. Our equation provides a unifying picture of the effects of recoil and indistinguishability of atoms beyond the Lamb-Dicke regime on both their dissipative and conservative dynamics. We give general expressions for the decay rates and the dipole-dipole shifts for any motional states, generalizing those in Ref. [1]. We find closed-form formulas for a number of relevant states (gaussian states, Fock states and thermal
states). In particular, we show that dipole-dipole interactions and cooperative photon emission [2] can be modulated through the external state of motion. As an application of our general formalism, we study the spatial Pauli blocking of two fermionic atoms beyond the Lamb-Dicke regime [3].
[1] G. S. Agarwal, Springer Tracts In Modern Physics 70, 1 (1974).
[2] R. H. Dicke, Phys. Rev. 93, 99 (1954).
[3] R. M. Sandner, M. Müller, A. J. Daley & P. Zoller, Phys. Rev. A 84, 043825 (2011)
Spectral Theory of Non-Markovian Dissipative Phase Transitions
To date, dissipative phase transitions (DPTs) have mostly been studied for
quantum systems coupled to idealized Markovian (memoryless) environments, where
the closing of the Liouvillian gap constitutes a hallmark. Here, we extend the
spectral theory of DPTs to arbitrary non-Markovian systems and present a
general and systematic method to extract their signatures, which is fundamental
for the understanding of realistic materials and experiments such as in the
solid-state, cold atoms, cavity or circuit QED. We first illustrate our theory
to show how memory effects can be used as a resource to control phase
boundaries in a model exhibiting a first-order DPT, and then demonstrate the
power of the method by capturing all features of a challenging second-order DPT
in a two-mode Dicke model for which previous attempts had fail up to now
Atom-only descriptions of the driven dissipative Dicke model
Funding: F.D. and A.D. acknowledge support from the EPSRC Programme Grant Des-OEQ (EP/P009565/1), and by the EOARD via AFOSR grant number FA9550-18-1-0064. J. K. acknowledges support from SU2P.We investigate how to describe the dissipative spin dynamics of the driven dissipative Dicke model, describing N two-level atoms coupled to a cavity mode, after adiabatic elimination of the cavity mode. To this end, we derive a Redfield master equation which goes beyond the standard secular approximation and large detuning limits. We show that the secular (or rotating wave) approximation and the large detuning approximation both lead to inadequate master equations, that fail to predict the Dicke transition or the damping rates of the atomic dynamics. In contrast, the full Redfield theory correctly predicts the phase transition and the effective atomic damping rates. Our work provides a reliable framework to study the full quantum dynamics of atoms in a multimode cavity, where a quantum description of the full model becomes intractable.PostprintPeer reviewe
Spin-orbit-assisted electron pairing in 1D waveguides
Understanding and controlling the transport properties of interacting
fermions is a key forefront in quantum physics across a variety of experimental
platforms. Motivated by recent experiments in 1D electron channels written on
the / interface, we analyse how the
presence of different forms of spin-orbit coupling (SOC) can enhance electron
pairing in 1D waveguides. We first show how the intrinsic Rashba SOC felt by
electrons at interfaces such as / can be
reduced when they are confined in 1D. Then, we discuss how SOC can be
engineered, and show using a mean-field Hartree-Fock-Bogoliubov model that SOC
can generate and enhance spin-singlet and triplet electron pairing. Our results
are consistent with two recent sets of experiments [Briggeman et al.,
arXiv:1912.07164; Sci. Adv. 6, eaba6337 (2020)] that are believed to engineer
the forms of SOC investigated in this work, which suggests that metal-oxide
heterostructures constitute attractive platforms to control the collective spin
of electron bound states. However, our findings could also be applied to other
experimental platforms involving spinful fermions with attractive interactions,
such as cold atoms.Comment: 12 pages, 7 figure
Dissipative quantum phase transition in an interacting manyparticle system: from two-level to multilevel spins
The dissipative Lipkin-Meshkov-Glick model of N all-to-all interacting two-level systems subject to collective and/or individual decay is known to display a dissipative phase transition. There, the collective or individual nature of the dissipation defines the order of the phase transition and the characteristics of the different phases, while having no impact on the position of the critical point.
Here, we investigate a generalization of this model to d-level spins (d ≥ 2). While basic features of the transition, such as the critical point, remain identical to the two-level case, the spin expectation values that characterize the different phases become ever more distinct from each other as d increases. Furthermore, depending on the exact form of the dissipator, the critical point transforms into a critical region that grows with d. Around the phase transition, the steady state of the system is entangled, and different choices of the dissipator may lead to a suppression or even an enhancement of entanglement by the individual dissipation
Master equation for collective spontaneous emission with quantized atomic motion
We derive a markovian master equation for the internal dynamics of an
ensemble of two-level atoms including all effects related to the quantization
of their motion. Our equation provides a unifying picture of the consequences
of recoil and indistinguishability of atoms beyond the Lamb-Dicke regime on
both their dissipative and conservative dynamics, and applies equally well to
distinguishable and indistinguishable atoms. We give general expressions for
the decay rates and the dipole-dipole shifts for any motional states, and we
find closed-form formulas for a number of relevant states (Gaussian states,
Fock states and thermal states). In particular, we show that dipole-dipole
interactions and cooperative photon emission can be modulated through the
external state of motion.Comment: 16 pages, 7 figures, minor correction
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