arXiv subjects

Makoto Yamaguchi

Publications and source records attributed to Makoto Yamaguchi.

13 recordsLinked to original sources

arXiv2022

Time-resolved physical spectrum in cavity quantum electrodynamics

The time-resolved physical spectrum of luminescence is theoretically studied for a standard cavity quantum electrodynamics system. In contrast to the power spectrum for the steady state, the correlation functions up to the present time are crucial for the construction of the time-resolved spectrum, while the correlations with future quantities are inaccessible because of the causality, i.e., the future quantities cannot be measured until the future comes. We find that this causality plays a key role to understand the time-resolved spectrum, in which the Rabi doublet can never be seen during the time of the first peak of the Rabi oscillation. Furthermore, the causality can influence on the transient magnitude of the Rabi doublet in some situations. We also study the dynamics of the Fano anti-resonance, where the difference from the Rabi doublet can be highlighted.

quant-ph↗

arXiv2021

Theory of Fano effect in cavity quantum electrodynamics

We propose a Markovian quantum master equation that can describe the Fano effect directly, by assuming a standard cavity quantum electrodynamics system. The framework allows us to generalize the Fano formula, applicable over the weak and strong coupling regimes with pure dephasing. A formulation of its emission spectrum is also given in a consistent manner. We then find that the interference responsible for the Fano effect is robust against pure dephasing. This is counterintuitive because the impact of interference is, in general, severely reduced by decoherence processes. Our approach thus provides a basis for theoretical treatments of the Fano effect and new insights into the quantum interference in open quantum systems.

quant-ph↗

arXiv2019

Fluctuation theorem in cavity quantum electrodynamics systems

We derive an integral fluctuation theorem (FT) in a general setup of cavity quantum electrodynamics systems. In the derivation, a key difficulty lies in a diverging behavior of entropy change arising from the zero-temperature limit of an external bath, which is required to describe the cavity loss. We solve this difficulty from the viewpoint of absolute irreversibility and find that two types of absolute irreversibility contribute to the integral FT. Furthermore, we show that, in a stationary and small cavity-loss condition, these contributions have simple relationships to the average number of photons emitted out of the cavity, and the integral FT yields an approximate form independent of the setup details. We illustrate the general results with a numerical simulation in a model of quantum heat engine.

cond-mat.stat-mech↗

arXiv2017

Decomposition of radiation energy into work and heat

We investigate energy transfer by the radiation from a cavity quantum electrodynamics (QED) system in the context of quantum thermodynamics. We propose a method of decomposing it into work and heat within the framework of quantum master equations. We find that the work and heat correspond respectively to the coherent and incoherent parts of the radiation. In the derivation of the method, it is crucial to investigate the dynamics of the system that receives the radiation from the cavity.

cond-mat.stat-mech↗

arXiv2017

Markovian Quantum Master Equation beyond Adiabatic Regime

By introducing a temporal change timescale $τ_{\text{A}}(t)$ for the time-dependent system Hamiltonian, a general formulation of the Markovian quantum master equation is given to go well beyond the adiabatic regime. In appropriate situations, the framework is well justified even if $τ_{\text{A}}(t)$ is faster than the decay timescale of the bath correlation function. An application to the dissipative Landau-Zener model demonstrates this general result. The findings are applicable to a wide range of fields, providing a basis for quantum control beyond the adiabatic regime.

cond-mat.stat-mech↗

arXiv2016

High-energy side-peak emission of exciton-polariton condensates in high density regime

In a standard semiconductor laser, electrons and holes recombine via stimulated emission to emit coherent light, in a process that is far from thermal equilibrium. Exciton-polariton condensates -- sharing the same basic device structure as a semiconductor laser, consisting of quantum wells coupled to a microcavity -- have been investigated primarily at densities far below the Mott density for signatures of Bose-Einstein condensation. At high densities approaching the Mott density, exciton-polariton condensates are generally thought to revert to a standard semiconductor laser, with the loss of strong coupling. Here, we report the observation of a photoluminescence sideband at high densities that cannot be accounted for by conventional semiconductor lasing. This also differs from an upper-polariton peak by the observation of the excitation power dependence in the peak-energy separation. Our interpretation as a persistent coherent electron-hole-photon coupling captures several features of this sideband whereas many remain elusive. Understanding the observation will lead to a development in non-equilibrium many-body physics.

cond-mat.quant-gas↗

arXiv2015

Generating Functional Approach for Spontaneous Coherence in Semiconductor Electron-Hole-Photon Systems

Electrons, holes, and photons in semiconductors are interacting fermions and bosons. In this system, a variety of ordered coherent phases can be formed through the spontaneous phase symmetry breaking because of their interactions. The Bose-Einstein condensation (BEC) of excitons and polaritons is one of such coherent phases, which can potentially crossover into the Bardeen-Cooper-Schrieffer (BCS) type ordered phase at high densities under quasi-equilibrium conditions, known as the BCS-BEC crossover. In contrast, one can find the semiconductor laser, superfluorescence (SF), and superradiance as relevant phenomena under nonequilibrium conditions. In this paper, we present a comprehensive generating functional theory that yields nonequilibrium Green's functions in a rigorous way. The theory gives us a starting point to discuss these phases in a unified view with a diagrammatic technique. Comprehensible time-dependent equations are derived within the Hartree-Fock approximation, which generalize the Maxwell-Semiconductor-Bloch equations under the relaxation time approximation. With the help of this formalism, we clarify the relationship among these cooperative phenomena and we show theoretically that the Fermi-edge SF is directly connected to the e-h BCS phase. We also discuss the emission spectra as well as the gain-absorption spectra.

cond-mat.mes-hall↗

arXiv2014

Equilibrium to nonequilibrium condensation in driven-dissipative semiconductor systems

Semiconductor microcavity systems strongly coupled to quantum wells are now receiving a great deal of attention because of their ability to efficiently generate coherent light by the Bose-Einstein condensation (BEC) of an exciton-polariton gas. Since the exciton polaritons are composite quasi-bosonic particles, many fundamental features arise from their original constituents, i.e., electrons, holes and photons. As a result, not only equilibrium phases typified by the BEC but also nonequilibrium lasing phases can be achieved. In this contribution, we describe a framework which can treat such equilibrium and nonequilibrium phases in a unified way.

cond-mat.mes-hall↗

arXiv2014

Second Thresholds in BEC-BCS-Laser Crossover of Exciton-Polariton Systems

The mechanism of second thresholds observed in several experiments is theoretically revealed by studying the BEC-BCS-laser crossover in exciton-polariton systems. We found that there are two different types for the second thresholds; one is a crossover within quasi-equilibrium phases and the other is into non-equilibrium (lasing). In both cases, the light-induced band renormalization causes gaps in the conduction and valence bands, which indicates the exsistence of bound electron-hole pairs in contrast to earlier expectations. We also show that these two types can be distinguished by the gain spectra.

cond-mat.mes-hall↗

arXiv2014

Cavity-loss induced plateau in coupled cavity QED array

Nonequilibrium steady states are investigated in a coupled cavity QED array system which is pumped by a thermal bath and dissipated through cavity loss. In the coherent (non-zero photon amplitude) phase, plateau regions appear, where the steady states become unchanged against the variation of the chemical potential of the thermal bath. The cavity loss plays a crucial role for the plateaus: the plateaus appear only if the cavity loss exists, and the photon leakage current, which is induced by the loss, is essential to the mechanism of the plateaus.

quant-ph↗

arXiv2013

First-order superfluid-Mott-insulator transition for quantum optical switching in cavity QED arrays with two cavity modes

We theoretically investigated the ground states of coupled arrays of cavity quantum electrodynamical (cavity QED) systems in presence of two photon modes. Within the Gutzwiller-type variational approach, we found the first-order quantum phase transition between Mott insulating and superfluid phases as well as the conventional second-order one. The first-order phase transition was found only for specific types of emitter models, and its physical origin is clarified based on the analytic arguments which are allowed in the perturbative and semiclassical limits. The first-order transition of the correlated photons is accompanied with discontinuous change in the emitter states, not only with the appearance of inter-cavity coherence in the superfluid phase. We also discuss the condition for the first-order transition to occur, which can lead to a strategy for future design of quantum optical switching devices with cavity QED arrays.

cond-mat.quant-gas↗

arXiv2011

Photonic Quantum Computation with Waveguide-Linked Optical Cavities and Quantum Dots

We propose a new scheme for solid-state photonic quantum computation in which trapped photons in optical cavities are taken as a quantum bit. Quantum gates can be realized by coupling the cavities with quantum dots through waveguides. The proposed scheme allows programmable and deterministic gate operations and the system can be scaled up to many quantum bits.

quant-ph↗

arXiv2009

Quantum Electrodynamics of a Nanocavity Coupled with Exciton Complexes in a Quantum Dot

Here, a comprehensive theory of the couplings between a nanocavity and exciton complexes in a quantum dot is developed, which successfully predicts the spectral triplet in the strong coupling regime that has been observed in several experiments but is unexpected according to conventional cavity quantum electrodynamics. The quantum anti-Zeno effect is found to play an essential role in the appearance of the central peak in the triplet under a low-excitation regime. The effect of hyperfine interactions is also discussed, which results in the cavity-mediated mixing of bright and dark exciton states. These results provide significant insights into solid-state cavity quantum electrodynamics.

quant-ph↗