arXiv subjects

Qingtian Miao

Publications and source records attributed to Qingtian Miao.

6 recordsLinked to original sources

arXiv2026

Quantum nonreciprocity from qubits coupled by Dzyaloshinskii-Moriya interaction

We present a theoretical study of quantum nonreciprocity induced via a Dzyaloshinskii-Moriya interaction (DMI) in an otherwise achiral, waveguide quantum electrodynamics. Using the full quantum master equation and input-output formalism for two-level systems coupled to a one-dimensional waveguide and driven by a coherent field, we show that an engineered DMI enables strong nonreciprocity in an otherwise reciprocal system, with tunable behavior governed by driving strength, detunings, and phase of the DMI. Using it not only demonstrates nonreciprocal transmission but also demonstrates nonreciprocal quantum entanglement and photon bunching. The system can end up in a pure state as certain decohering channels do not participate. The pure state leads to power-independent perfect transparency. Conditions are derived and depend on the propagation phase, the relative detuning of the two qubits, and the exchange interaction. At these pure-state points, the steady-state entanglement is reciprocal and admits a closed-form expression; away from them, phase control generates strong entanglement nonreciprocity. The DMI also reshapes photon statistics, redistributing two-photon correlations and shifting superbunching from transmission (no DMI) to reflection at finite DMI. These results establish DMI as a versatile resource for engineering nonreciprocity, transparency, entanglement, and photon correlations in waveguide QED, enabling isolators, routers, and superbunching light sources without requiring chiral waveguides.

quant-ph↗

arXiv2025

Time crystals and nonequilibrium dissipative phase transitions mediated by squeezed bath

Nonequilibrium dissipative phase transition, arising from the competition of cooperative behavior and coherent field driving, discovered in the 1970s by Narducci et al. and Walls et al., has been found to exhibit time-crystal behavior when the driving field exceeds the cooperative decay rate. This was seen through the study of the eigenvalues of the Liouvillian superoperator that describes the joint effect of drive and cooperativity. The cooperative decay depends on the nature of the reservoir correlations. If the reservoir correlations have phase-sensitive behavior, then the eigenvalues of the Liouvillian will be different. We investigate the time-crystal behavior of the nonequilibrium dissipative phase transitions under the influence of a squeezed vacuum reservoir. We analyze the steady-state phase diagram as a function of the control parameter and demonstrate that increasing the squeezing strength sharpens the dissipative phase transition. Spectral analysis of the Liouvillian reveals gap closings and the emergence of purely imaginary eigenvalues in the thermodynamic limit, indicating the time-crystal phase. We find that the real parts of subleading eigenvalues exhibit nonmonotonic behavior with increasing squeezing, reflecting the sensitivity of relaxation dynamics to the reservoir properties. Time-domain simulations confirm that the oscillation frequencies correspond to the imaginary parts of the Liouvillian eigenvalues. We also present results on quantum fluctuations in the time-crystal phase. Our results call attention to the study of time crystals in models of cooperativity based on engineered environments.

quant-ph↗

arXiv2024

Transparency, Nonclassicality and Nonreciprocity in Chiral Waveguide Quantum Electrodynamics

We examine quantum statistical properties of transmission and reflection from a chiral waveguide coupled to qubits for arbitrary input powers. We report on several remarkable features of output fields such as transparency, quantum nonreciprocity and the second-order correlation function $g^{(2)}(0)$ values less than unity. In particular, for two qubits detuned antisymmetrically with respect to the central waveguide frequency, we find transparency in forward transmission and in photon numbers for arbitrary values of the input powers provided the phase separation between qubits is an integer multiple of $π$. Values of $g^{(2)}(0)$ less than unity can be reached even for nonzero value of the intrinsic damping by using phase separation different from integer multiple of $π$, marking the transition from classical to quantum light. We also uncover a new type of quantum criticality that enables complete suppression of forward-propagating amplitude transmission at specific driving powers, giving rise to enhanced nonreciprocal effects in both transmission and quantum fluctuations in amplitudes. Forward propagation amplifies the quantum fluctuations in amplitudes, while backward propagation significantly suppresses them. These findings open new pathways for controlling light-matter interactions in chiral quantum electrodynamics, with potential applications in quantum information and nonreciprocal quantum devices.

quant-ph↗

arXiv2024

Kerr Nonlinearity Induced Nonreciprocity in dissipatively coupled resonators

Nonlinearity induced nonreciprocity is studied in a system comprising two resonators coupled to a one-dimensional waveguide when the linear system does not exhibit nonreciprocity. The analysis is based on the Hamiltonian of the coupled system and includes the dissipative coupling between the waveguide and resonators, along with the input-output relations. We consider a large number of scenarios which can lead to nonreciprocity. We pay special attention to the case when the linear system does not exhibit nonreciprocal behavior. In this case, we show how very significant nonreciprocal behavior can result from Kerr nonlinearities. We find that the bistability of the nonlinear system can aid in achieving large nonreciprocity. Additionally, We bring out nonreciprocity in the excitation of each resonator, which can be monitored independently. Our results highlight the profound influence of nonlinearity on nonreciprocal behavior, offering a new avenue for controlling light propagation in integrated photonic circuits. Nonlinearity induced nonreciprocity would lead to significant nonreciprocity in quantum fluctuations when our system is treated quantum mechanically.

physics.optics↗

arXiv2023

Engineering bound states in continuum via nonlinearity induced extra dimension

Bound states in continuum (BICs) are localized states of a system possessing significantly large life times with applications across various branches of science. In this work, we propose an expedient protocol to engineer BICs which involves the use of Kerr nonlinearities in the system. The generation of BICs is a direct artifact of the nonlinearity and the associated expansion in the dimensionality of the system. In particular, we consider single and two mode anharmonic systems and provide a number of solutions apposite for the creation of BICs. In close vicinity to the BIC, the steady state response of the system is immensely sensitive to perturbations in natural frequencies of the system and we illustrate its propitious sensing potential in the context of experimentally realizable setups for both optical and magnetic nonlinearities.

quant-ph↗

arXiv2023

Polaritonic Ultrastrong Coupling: Quantum Entanglement in Ground State

The ultrastrong coupling between the elementary excitations of matter and microcavity modes is studied in a fully analytical quantum-mechanical theoretical framework. The elementary excitation could be phonons, excitons, plasmons, etc. From the diagonalization of the Hamiltonian, we obtain the ground state of the polariton Hamiltonian. The ground state belongs to the Gaussian class. Using the Gaussian property we calculate the quantum entanglement in the ground state. We use two different measures for quantum entanglement -- entanglement entropy and the logarithmic negativity parameter and obtain rather simple analytical expressions for the entanglement measures. Our findings show that the amount of quantum entanglement in the ground state is quite significant in the ultrastrong coupling regime. It can be obtained from the measurement of the polariton frequencies.

quant-ph↗