arXiv subjects

Jinshuang Jin

Publications and source records attributed to Jinshuang Jin.

At least 19 recordsLinked to original sources

arXiv2026

Temperature--Hamiltonian Ambiguity in Strong-Coupling Quantum Equilibrium

Strong coupling generally drives a subsystem away from the Gibbs state of its bare Hamiltonian at the bath temperature. We formulate a temperature--Hamiltonian ambiguity: the reduced equilibrium state fixes the dimensionless Gibbs generator, but does not by itself uniquely determine the local Hamiltonian and temperature entering a Gibbs representation. We propose an operational resolution in which the local Hamiltonian is identified from physical information independent of the stationary Gibbs parametrization. Whenever the exact reduced state is compatible with the Gibbs family generated by that independently identified Hamiltonian, it then determines a unique local temperature. An exactly solvable two-level-system--oscillator model makes the ambiguity explicit through state-equivalent descriptions based on temperature renormalization relative to a specified local Hamiltonian and Hamiltonian-of-mean-force level renormalization at the bath temperature. An exact bosonic model provides the complementary case in which retarded dynamics independently fixes a renormalized local excitation scale and thereby specifies the local Hamiltonian before the stationary populations determine the temperature. These results distinguish state representation from thermodynamic assignment and provide an operational framework for local thermodynamics beyond weak coupling.

quant-ph↗

arXiv2026

Coulomb interaction unlocks Majorana-mediated electron teleportation between Quantum dots

We investigate quantum transport in a hybrid system composed of two quantum dots (QDs) coupled through a pair of spatially separated Majorana zero modes (MZMs) with negligible coupling energy. We focus on nonlocal correlations mediated by the MZMs, particularly the role of Coulomb interaction U between the QDs and the Majorana wire. Using the numerically exact fermionic dissipation equation of motion (DEOM) method, we compute both the transient current and the current-current cross-correlation noise spectrum. In the non-interacting case (U=0), destructive interference between the degenerate normal tunneling and anomalous tunneling channels suppresses electron teleportation between the dots. Introducing a finite Coulomb interaction $U$ lifts this channel degeneracy, enabling strong nonlocal correlations and inter-dot electron teleportation. This effect manifests as a robust signal in the cross-correlation noise spectrum, which is significantly stronger than that induced by a finite Majorana coupling energy $\varepsilon_{M}$. Our findings propose Coulomb interaction as an efficient and experimentally accessible control parameter for generating and detecting Majorana-mediated nonlocal transport in the topologically relevant long-wire limit ($\varepsilon_{M}\rightarrow0$).

cond-mat.mes-hall↗

arXiv2025

Phase-controlled quantum transport signatures in a quantum dot-Majorana hybrid ring system

We investigate the quantum transport in a hybrid ring system consisting of a quantum dot (QD) coupled to two Majorana bound states (MBSs) hosted in a topological superconducting nanowire, threaded by a magnetic flux. Utilizing the dissipaton equation-of-motion approach, we demonstrate that the differential conductance shows periodic behavior and its periodicity depends on both the QD energy level and the MBS overlapping. A zero-bias peak (ZBP) emerges as a result of the balance between normal and anomalous tunneling processes, associated with the presence of a single MBS. Beyond the phase-dependent periodic behavior, the shot noise exhibits voltage-dependent transitions between sub-Poissonian ($F = 0.5$), Poissonian ($F = 1$), and super-Poissonian ($F > 1$) regimes. Strikingly, we find a giant Fano factor ($F\gg1$) emerging at the balance point, accompanied by a peak in the shot noise. This distinctive feature may serve as a supplementary signature for MBS detection. However, both ZBP in the differential conductance and shot noise peak are degraded by thermal effects.

cond-mat.mes-hall↗

arXiv2025

Majorana qubit readout by a point-contact detector under finite bias voltages

In this work we revisit the problem of a Majorana box qubit (MBQ) readout by a point-contact (PC) detector. The logic states of the MBQ are associated with the combined fermion parities of the MBQ and its tunnel-coupled quantum dot, which is measured by a PC detector. Beyond the existing studies on limiting bias voltage regimes, we analyze the steady-state current and the current power spectrum across all bias voltages. Our results indicate that the MBQ readout via the parity-dependent detector current is effective only at low bias voltage regime and requires the dot energy level to be off-resonance with the Majorana qubit. In contrast, the current power spectrum allows MBQ readout through the parity-dependent Rabi oscillation peak signals for arbitrary bias voltages, without restrictions on the dot energy level. Particularly, with focus on the MBQ measurement visibility, we analyze the peak-to-pedestal ratio for each characteristic peak (associated with each logic state of the qubit) and the signal-to-noise ratio of the two peaks. By examining these two metrics, we identify the optimal bias voltage window for the PC detector at low temperature limit.

cond-mat.mes-hall↗

arXiv2025

Distinguishing Majorana bound states from Andreev bound states through differential conductance and current noise spectrum

We investigate the quantum transport through a quantum dot coupled with a superconducting (SC) nanowire. By elaborating the differential conductance and current noise spectrum, we focus on the distinct characteristics of the topological Majorana bound states (MBSs) and trivial Andereev bound states (ABSs) hosted in SC wire. For MBSs with a topological quality factor $q=1$, we observe the degenerate features manifested as the zero-bias peak (ZBP) in differential conductance and the Rabi dips degeneracy (RDD) in noise spectrum. In contrast, for ABSs with $q<1$, the splitting of these degenerate features depends on the linewidth, arising from realistic measurement conditions. Furthermore, we identify the critical quality factors $q_{\rm c}$ and $q_{\rm s}$ associated with the emergences of ZBP and RDD, respectively. The value of $q_{\rm c}$ is temperature-dependent, and we establish a suitable temperature window to ensure the visibility of single ZBP in the experiments. Whereas, $q_{\rm c}$ depends on the coupling strength rather than the temperature. Typical values for these quality factors are approximately $q_{\rm c}\approx 0.93$ and $q_{\rm s}\approx 0.99$. Our results suggest that the degenerate Rabi spectrum signal could serve as a hallmark for the presence of MBSs, which goes beyond the scope of differential conductance.

cond-mat.mes-hall↗

arXiv2024

Bubble dynamics in the Polyakov quark-meson model

In the framework of the Polyakov quark-meson model with two flavors, the bubble dynamics of a first-order phase transition in the region of high density and low temperature are investigated by using the homogeneous thermal nucleation theory. In mean-field approximation, after obtaining the effective potential with inclusion of the fermionic vacuum term, we build a geometric method to search two existing minima, which can be actually connected by a bounce interpolated between a local minimum to an adjacent global one. For both weak and strong first-order hadron quark phase transitions, as fixing the chemical potentials at $μ=306 \mathrm{MeV}$ and $μ=310 \mathrm{MeV}$, the bubble profiles, the surface tension, the typical radius of the bounce and the saddle point action as a function of temperature are numerically calculated in the presence of a nucleation bubble. It is found that the surface tension remains a very small value even when the density is high. It is also noticed that the deconfinement phase transition does not change chiral phase transition dramatically for light quarks and phase boundaries for hadron and quark matter should be resized properly according to the saddle-point action evaluated on the bounce solution.

hep-ph↗

arXiv2022

Master equation approach for transport through Majorana zero modes

Based on an exact formulation, we present a master equation approach to transport through Majorana zero modes (MZMs). Within the master equation treatment, the occupation dynamics of the regular fermion associated with the MZMs holds a quite different picture from the BdG S-matrix scattering process, in which the "positive" and "negative" energy states are employed, while the master equation treatment does not involve them at all. Via careful analysis for the structure of the rates and the rate processes governed by the master equation, we reveal the intrinsic connection between both approaches. This connection enables us to better understand the confusing issue of teleportation when the Majorana coupling vanishes. We illustrate the behaviors of transient rates, occupation dynamics and currents. Through the bias voltage dependence, we also show the Markovian condition for the rates, which can extremely simplify the applications in practice. As future perspective, the master equation approach developed in this work can be applied to study important time-dependent phenomena such as photon-assisted tunneling through the MZMs and modulation effect of the Majorana coupling energy.

cond-mat.mes-hall↗

arXiv2022

Memory effect preserved time-local approach to noise spectrum of transport current

Within the second-order non-Markovian master equation description, we develop an efficient method for calculating the noise spectrum of transport current through interacting mesoscopic systems. By introducing proper current-related density operators, we propose a practical and very efficient time-local approach to compute the noise spectrum, including the asymmetric spectrum, which contains the full information of energy emission and absorption. We obtain an analytical formula of the current noise spectrum to characterize the nonequilibrium transport including electron-electron Coulomb interaction and the memory effect. We demonstrate the proposed method in transport through interacting-quantum-dots system, and find good agreement with the exact results under broad range of parameters.

cond-mat.mes-hall↗

arXiv2021

Majorana Conductances in Three-Terminal Transports

We consider a two-lead (three-terminal) setup of nonlocal transport through Majorana zero modes (MZMs) and construct a Majorana master equation (which is also valid for small bias voltage). We first carry out representative results of current and then show that a modified Bogoliubov-de Gennes (BdG) treatment can consistently recover the same results. Based on the interplay of the two approaches, we reveal the existence of nonvanishing channels of teleportation and crossed Andreev reflections even at the limit $ε_M\to 0$ (zero coupling energy of the MZMs), which leads to new predictions for the height of the zero-bias-peak of the local conductance and the $ε_M$-scaling behavior of the teleportation conductance, for verification by experiments.

cond-mat.mes-hall↗

arXiv2020

Mechanism of current noise spectrum in a nonequilibirum Kondo dot system

We systematically study the nonequilibirum Kondo mechanisms of quantum noise spectrum based on the accurate dissipaton--equation--of--motion evaluations. By comparing the noise spectra between the equilibrium and nonequilibrium cases and between the non-Kondo and Kondo regimes, we identify the nonequilibrium Kondo features in the current noise spectrum, appearing in the region of $ω\in [-eV, eV]$. The Kondo characteristic at $ω=\pm eV=\pm (μ_{\rm L}-μ_{\rm R})$ display asymmetrical upturns and remarkable peaks in $S(ω)$ and $dS(ω)/dω$, respectively. These features are originated from the Rabi interference of the transport current dynamics, with the Kondo oscillation frequency of $|eV|$. The minor but very distinguishable inflections, crossing over $ω=-eV$ to $ω=+eV$, would be related to a sort of Kondo-Fano interference between two Kondo resonances channels.

cond-mat.mes-hall↗

arXiv2019

Nonequilibirum noise spectrum and Coulomb-blockade-assisted Rabi interference in a double-dot Aharonov-Bohm interferometer

We investigate the charge-states coherence underlying the nonequilibirum transport through a spinless double-dot Aharonov-Bohm (AB) interferometer. Both the current noise spectrum and real-time dynamics are evaluated with the well-established dissipaton-equation-of-motion method. The resulted spectrums show the characteristic peaks and dips, arising from coherent Rabi oscillation dynamics, with the environment-assisted indirect inter-dot tunnel coupling mechanism. The observed spectroscopic features are in a quantitative agreement to the real-time dynamics of the reduced density matrix off-diagonal element between two charge states. As the aforementioned mechanism, these characteristics of coherence are very sensitive to the AB phase. While this is generally true for cross-correlation spectrum, the total circuit noise spectrum that is experimentally more accessible shows remarkably rich interplay between various mechanisms. The most important finding of this work is the existence of Coulomb-blockade-assisted Rabi interference, with very distinct signatures arising from the interplay between the AB interferometer and the interdot Coulomb interaction induced Fano resonance.

cond-mat.mes-hall↗

arXiv2017

Manipulating quantum coherence of charge states in interacting double-dot Aharonov-Bohm interferometers

We investigate the dynamics of charge--states coherence in a degenerate double--dot Aharonov--Bohm interferometer with finite interdot Coulomb interactions. The quantum coherence of the charge states is found to be sensitive to the transport setup configurations, involving both the single--electron impurity channels and the Coulomb--assisted ones. We numerically demonstrate the emergence of a complete coherence between the two charge states, with the relative phase being continuously controllable through the magnetic flux. Remarkably, a fully coherent charge qubit arises at the double--dots electron pair tunneling resonance condition, where the chemical potential of one electrode is tuned at the center between a single--electron impurity channel and the related Coulomb--assisted channel. This pure quantum state of charge qubit could be \emph{experimentally located} at the current--voltage characteristic turnover position, where differential conductance sign changes. We further elaborate the underlying mechanism for both the real--time and the stationary charge--states coherences in the double--dot systems of study.

cond-mat.mes-hall↗

arXiv2017

Experimental simulation of quantum temporal steering beyond rotating-wave approximation

Characterizing the dynamics of open systems usually starts with a perturbative theory and involves various approximations, such as the Born, Markov and rotating-wave approximation (RWA). However, the approximation approaches could introduce more or less incompleteness in describing the bath behaviors. Here, we consider a quantum channel, which is modeled by a qubit (a two-level system) interacting with a bosonic bath. Unlike the traditional works, we experimentally simulate the system-bath interaction without applying the Born, Markov, and rotating-wave approximations. To our knowledge, this is the first experimental simulation of the quantum channels without any approximations mentioned above, by using linear optical devices. The results are quite useful and interesting, which not only reveal the effect of the counter-rotating terms but also present a more accurate picture of the quantum channel dynamics. Besides, we experimentally investigate the dynamics of the quantum temporal steering (TS), i.e., a temporal analogue of Einstein-Podolsky-Rosen steering. The experimental and theoretical results are in good agreement and show that the counter-rotating terms significantly influence the TS dynamics. When one monogamously associates TS with the security of the cryptographic protocols (e.g., BB84), our experimental tests reveal that the channels based on RWA will provide exaggerated security durations, while they are actually insecure in non-RWA channel cases. This implies that doing RWA may result in a risk for the security of quantum key distribution. Our findings are expected to have useful applications in secure quantum communications and future interesting TS studies.

quant-ph↗

arXiv2015

Nontopological Soliton in the Polyakov Quark Meson Model

Within a mean field approximation, we study a nontopological soliton solution of the Polyakov quark-meson model in the presence of a fermionic vacuum term with two flavors at finite temperature and density. The profile of the effective potential exhibits a stable soliton solution below a critical temperature $T\leq T_χ^c$ for both the crossover and the first-order phase transitions, and these solutions are calculated here with appropriate boundary conditions. However, it is found that only if $T\leq T^c_d$,the energy of the soliton $M_N$ is less than the energy of the three free constituent quarks $3M_q$. As $T> T^c_d$, there is an instant delocalization phase transition from hadron matter to quark matter. The phase diagram together with the location of a critical end point (CEP) has been obtained in $T$ and $μ$ plane. We notice that two critical temperatures always satisfy $T^c_d\leq T_χ^c$. Finally, we present and compare the result of thermodynamic pressure at zero chemical potential with lattice data.

hep-ph↗

arXiv2015

Non-Markovian correlation functions for open quantum systems

Beyond the conventional quantum regression theorem, a general formula for non-Markovian correlation functions of arbitrary system operators both in the time- and frequency-domain is given. We approach the problem by transforming the conventional time-nonlocal master equation into dispersed time-local equations-of-motion. The validity of our approximations is discussed and we find that the non-Markovian terms have to be included for short times. While calculations of the density matrix at short times suffer from the initial value problem, a correlation function has a well defined initial state. The resulting formula for the non-Markovian correlation function has a simple structure and is as convenient in its application as the conventional quantum regression theorem for the Markovian case. For illustrations, we apply our method to investigate the spectrum of the current fluctuations of interacting quantum dots contacted with two electrodes. The corresponding non-Markovian characteristics are demonstrated.

quant-ph↗

arXiv2015

Unraveling of a generalized quantum Markovian master equation and its application in feedback control of a charge qubit

In the context of a charge qubit under continuous monitoring by a single electron transistor, we propose an unraveling of the generalized quantum Markovian master equation into an ensemble of individual quantum trajectories for stochastic point process. A suboptimal feedback algorism is implemented into individual quantum trajectories to protect a desired pure state. Coherent oscillations of the charge qubit could be maintained in principle for an arbitrarily long time in case of sufficient feedback strength. The effectiveness of the feedback control is also reflected in the detector's noise spectrum. The signal-to-noise ratio rises significantly with increasing feedback strength such that it could even exceed the Korotkov-Averin bound in quantum measurement, manifesting almost ideal quantum coherent oscillations of the qubit. The proposed unraveling and feedback protocol may open up the prospect to sustain ideal coherent oscillations of a charge qubit in quantum computation algorithms.

cond-mat.mes-hall↗

arXiv2014

Electroluminescence and multi-photon effects in a resonator driven by a tunnel junction

We consider a transmission line resonator which is driven by electrons tunneling through a voltage-biased tunnel junction. Using the Born-Markovian quantum master equation in the polaron basis we investigate the nonequilibrium photon state and emission spectrum of the resonator as well as properties of the transport current across the tunnel junction and its noise spectrum. The electroluminescence is optimized, with maximum peak height and narrow linewidth, when the back-action of the tunnel junction on the resonator and the decay rate of the resonator are similar in strength. For strong coupling between the resonator and tunnel junction, multi-photon effects show up in the noise spectrum of the transport current.

cond-mat.mes-hall↗

arXiv2014

Improved master equation approach to quantum transport: From Born to self-consistent Born approximation

Beyond the second-order Born approximation, we develop an improved master equation approach to quantum transport by virtue of a self-consistent Born approximation. The basic idea is replacing the free Green's function in the tunneling self-energy by an effective reduced propagator under the Born approximation. We found that the effect of this simple improvement is remarkable, for instance, it can not only recover the exact result of noninteracting transport under arbitrary voltages, but also predict the challenging nonequilibrium Kondo effect. In addition to having an elegant structure, the application convenience and accuracy of the proposed scheme, as demonstrated by the examples in this work, may suggest it a useful tool for quantum transports.

cond-mat.mes-hall↗