arXiv subjects

Si-Yuan Bai

Publications and source records attributed to Si-Yuan Bai.

14 recordsLinked to original sources

arXiv2026

Floquet engineering in hybrid magnetic quantum systems

The advancement of magnonics has facilitated the utilization of hybrid magnetic systems in quantum technologies. A hybrid magnetic lattice formed by an array of superconducting loops and magnetic particles has been devised as a quantum bus to disseminate quantum resources among magnetic quantum entities serving as nodes of a quantum network. However, the lattice also exerts a decoherence effect on the quantum entities, which impairs its practical performance. By studying the non-Markovian dynamics of nitrogen-vacancy centers and magnon modes coupled to two independent hybrid magnetic lattices, we propose a Floquet-engineering scheme via periodic driving on the quantum entities to suppress decoherence. We find that significant steady-state entanglement is preserved when a Floquet bound state exists in the quasienergy spectrum of the system consisting of each driven quantum entity and its lattice. This result enables a precise manipulation of hybrid magnetic systems and benefits their applications in quantum networks.

quant-ph↗

arXiv2025

Long-Range Quantum Tunneling via Matter Wave

Quantum tunneling is a quantum phenomenon in which a microscopic object crosses through a potential barrier even if its energy cannot overcome the barrier. A general belief is that tunneling occurs only when the barrier width is comparable to, or smaller than the de Broglie's wavelength of the object. Here, we study the tunneling of an ultracold atom among $N$ far-separated trapping potentials in a state-selective optical lattice and present a mechanism to realize long-range tunneling. We find that, mediated by the propagating matter wave emitted from the atom, coherent tunneling of the atom to the remote lattices occurs as long as bound states are present in the energy spectrum of the system formed by the atom and its matter wave. Going beyond the Markovian approximation, and breaking through the conventional distance constraint, our result opens another avenue to realizing tunneling and gives a guideline to developing tunneling devices.

quant-ph↗

arXiv2024

Temperature-heat uncertainty relation in nonequilibrium quantum thermometry

We investigate the temperature uncertainty relation in nonequilibrium probe-based temperature estimation process. We demonstrate that it is the fluctuation of heat that fundamentally determines temperature precision through the temperature-heat uncertainty relation. Specifically, we find that heat is divided into trajectory heat and correlation heat, which are associated with the heat exchange along thermometer's evolution and the correlation between the thermometer and the sample, respectively. Based on two type of thermometers, we show that both of these heat terms are resources for enhancing temperature precision. By clearly distinguishing the resources for enhancing estimation precision, our findings not only explain why various quantum features are crucial for accurate temperature sensing but also provide valuable insights for designing ultrahigh-sensitive quantum thermometers. Additionally, we demonstrate that the temperature-heat uncertainty relation is consistent with the well-known temperature-energy uncertainty relation in thermodynamics. It establishes a connection between the information theory and the thermodynamics.

quant-ph↗

arXiv2024

Non-Markovian quantum interconnect formed by a surface plasmon polariton waveguide

Allowing the generation of effective interactions between distant quantum emitters (QEs) via flying photons, quantum interconnect (QI) is essentially a light-matter interface and acts as a building block in quantum technologies. A surface plasmon polariton (SPP) supported by a metallic waveguide provides an ideal interface to explore strong light-matter couplings and to realize QI. However, the loss of SPP in metal makes the mediated entanglement of the QEs damp with the increase of the distance and time, which hinders its applications. We propose a scheme of non-Markovian QI formed by the SPP of a metallic nanowire. A mechanism to make the generated entanglement of the QEs persistent is discovered. We find that, as long as bound states are formed in the energy spectrum of total QE-SPP system, the damping of the SPP-mediated entanglement is overcome even in the presence of the metal absorption to the SPP. Our finding enriches our understanding of light-matter couplings in absorptive medium and paves the way for using the SPP in designing QI.

quant-ph↗

arXiv2023

Quantum metrology in the noisy intermediate-scale quantum era

Quantum metrology pursues the physical realization of higher-precision measurements to physical quantities than the classically achievable limit by exploiting quantum features, such as entanglement and squeezing, as resources. It has potential applications in developing next-generation frequency standards, magnetometers, radar, and navigation. However, the ubiquitous decoherence in the quantum world degrades the quantum resources and forces the precision back to or even worse than the classical limit, which is called the no-go theorem of noisy quantum metrology and greatly hinders its applications. Therefore, how to realize the promised performance of quantum metrology in realistic noisy situations attracts much attention in recent years. We will review the principle, categories, and applications of quantum metrology. Special attention will be paid to different quantum resources that can bring quantum superiority in enhancing sensitivity. Then, we will introduce the no-go theorem of noisy quantum metrology and its active control under different kinds of noise-induced decoherence situations.

quant-ph↗

arXiv2023

Floquet Engineering to Overcome No-Go Theorem of Noisy Quantum Metrology

Permitting a more precise measurement to physical quantities than the classical limit by using quantum resources, quantum metrology holds a promise in developing many revolutionary technologies. However, the noise-induced decoherence forces its superiority to disappear, which is called no-go theorem of noisy quantum metrology and constrains its application. We propose a scheme to overcome the no-go theorem by Floquet engineering. It is found that, by applying a periodic driving on the atoms of the Ramsey spectroscopy, the ultimate sensitivity to measure their frequency characterized by quantum Fisher information returns to the ideal $t^2$ scaling with the encoding time whenever a Floquet bound state is formed by the system consisting of each driven atom and its local noise. Combining with the optimal control, this mechanism also allows us to retrieve the ideal Heisenberg-limit scaling with the atom number $N$. Our result gives an efficient way to avoid the no-go theorem of noisy quantum metrology and to realize high-precision measurements.

quant-ph↗

arXiv2022

Strong coupling of quantum emitters and the exciton polariton in MoS$_2$ nanodisks

As a quasiparticle formed by light and excitons in semiconductors, the exciton-polariton (EP) as a quantum bus is promising for the development of quantum interconnect devices at room temperature. However, the significant damping of EPs in the material generally causes a loss of quantum information. We propose a mechanism to overcome the destructive effect of a damping EP on its mediated correlation dynamics of quantum emitters (QEs). Via an investigation of the near-field coupling between two QEs and the EP in a monolayer MoS$_{2}$ nanodisk, we find that, with the complete dissipation of the QEs efficiently avoided, a persistent quantum correlation between the QEs can be generated and stabilized even to their steady state. This is due to the fact that, with upon decreasing the QE-MoS$_2$ distance, the QEs become so hybridized with the EP that one or two bound states are formed between them. Our result supplies a useful way to avoid the destructive impact of EP damping, and it refreshes our understanding of the light-matter interaction in absorbing medium.

cond-mat.mes-hall↗

arXiv2022

Temperature uncertainty relation in non-equilibrium thermodynamics

Temperature uncertainty of a quantum system in canonical ensemble is inversely determined by its energy fluctuation, which is known as the temperature-energy uncertainty relation. No such uncertainty relation was discovered for a non-equilibrium open quantum system. In this article, we derive a universal temperature uncertainty relation for general non-equilibrium processes. We find that it is the fluctuation of heat, which is defined as the change in bath energy, determines the temperature uncertainty in non-equilibrium case. Specifically, the heat is divided into trajectory heat and backaction heat, which are associated with the system's trajectory of evolution and the backaction of partial measurement on system, respectively. Based on this decomposition, we reveal that both correlations between system and bath's process function and state function are the resources for enhancing temperature precision. Our findings are conductive to design ultrahigh sensitive quantum thermometer.

quant-ph↗

arXiv2022

Non-Markovian quantum thermometry

The rapidly developing quantum technologies and thermodynamics have put forward a requirement to precisely control and measure the temperature of microscopic matter at the quantum level. Many quantum thermometry schemes have been proposed. However, precisely measuring low temperature is still challenging because the obtained sensing errors generally tend to diverge with decreasing temperature. Using a continuous-variable system as a thermometer, we propose non-Markovian quantum thermometry to measure the temperature of a quantum reservoir. A mechanism to make the sensing error $δT$ scale with the temperature $T$ as the Landau bound $δT\simeq T$ in the full-temperature regime is discovered. Our analysis reveals that it is the quantum criticality of the total thermometer-reservoir system that causes this enhanced sensitivity. Efficiently avoiding the error-divergence problem, our result gives an efficient way to precisely measure the low temperature of quantum systems.

quant-ph↗

arXiv2021

Generating stable spin squeezing by squeezed-reservoir engineering

As a genuine many-body entanglement, spin squeezing (SS) can be used to realize the highly precise measurement beyond the limit constrained by classical physics. Its generation has attracted much attention recently. It was reported that $N$ two-level systems (TLSs) located near a one-dimensional waveguide can generate a SS by using the mediation effect of the waveguide. However, a coherent driving on each TLS is used to stabilize the SS, which raises a high requirement for experiments. We here propose a scheme to generate stable SS resorting to neither the spin-spin coupling nor the coherent driving on the TLSs. Incorporating the mediation role of the common waveguide and the technique of squeezed-reservoir engineering, our scheme exhibits the advantages over previous ones in the scaling relation of the SS parameter with the number of the TLSs. The long-range correlation feature of the generated SS along the waveguide in our scheme may endow it with certain superiority in quantum sensing, e.g., improving the sensing efficiency of spatially unidentified weak magnetic fields.

quant-ph↗

arXiv2021

Threshold for a discrete-variable sensor of quantum reservoirs

Quantum sensing employs quantum resources of a sensor to attain a smaller estimation error of physical quantities than the limit constrained by classical physics. To measure a quantum reservoir, which is significant in decoherence control, a nonunitary-encoding sensing scheme becomes necessary. However, previous studies showed that the reservoir-induced degradation to quantum resources of the sensor makes the errors divergent with the increase of encoding time. We here propose a scheme to use $N$ two-level systems as the sensor to measure a quantum reservoir. A threshold, above which the shot-noise-limited sensing error saturates or even persistently decreases with the encoding time, is uncovered. Our analysis reveals that it is due to the formation of a bound state of the total sensor-reservoir system. Solving the outstanding error-divergency problem in previous studies, our result supplies an insightful guideline in realizing a sensitive measurement of quantum reservoirs.

quant-ph↗

arXiv2021

Non-Markovian Sensing of a Quantum Reservoir

Quantum sensing explores protocols using the quantum resource of sensors to achieve highly sensitive measurement of physical quantities. The conventional schemes generally use unitary dynamics to encode quantities into sensor states. In order to measure the spectral density of a quantum reservoir, which plays a vital role in controlling the reservoir-caused decoherence to microscopic systems, we propose a nonunitary-encoding optical sensing scheme. Although the nonunitary dynamics for encoding in turn degrades the quantum resource, we surprisingly find a mechanism to make the encoding time a resource to improve the precision and to make the squeezing of the sensor a resource to surpass the shot-noise limit. Our result shows that it is due to the formation of a sensor-reservoir bound state. Enriching the family of quantum sensing, our scheme gives an efficient way to measure the quantum reservoir and might supply an insightful support to decoherence control.

quant-ph↗

arXiv2021

Quantum Control in Open and Periodically Driven Systems

Quantum technology resorts to efficient utilization of quantum resources to realize technique innovation. The systems are controlled such that their states follow the desired manners to realize different quantum protocols. However, the decoherence caused by the system-environment interactions causes the states deviating from the desired manners. How to protect quantum resources under the coexistence of active control and passive decoherence is of significance. Recent studies have revealed that the decoherence is determined by the feature of the system-environment energy spectrum: Accompanying the formation of bound states in the energy spectrum, the decoherence can be suppressed. It supplies a guideline to control decoherence. Such idea can be generalized to systems under periodic driving. By virtue of manipulating Floquet bound states in the quasienergy spectrum, coherent control via periodic driving dubbed as Floquet engineering has become a versatile tool not only in controlling decoherence, but also in artificially synthesizing exotic topological phases. We will review the progress on quantum control in open and periodically driven systems. Special attention will be paid to the distinguished role played by the bound states and their controllability via periodic driving in suppressing decoherence and generating novel topological phases.

quant-ph↗

arXiv2020

Floquet Engineering to Reactivate a Dissipative Quantum Battery

As an energy storing and converting device near atomic size, a quantum battery (QB) promises enhanced charging power and extractable work using quantum resources. However, the ubiquitous decoherence causes its cyclic charging-storing-discharging process to become deactivated, which is called aging of the QB. Here, we propose a mechanism to overcome the aging of a QB. It is found that the decoherence of the QB is suppressed when two Floquet bound states (FBSs) are formed in the quasienergy spectrum of the total system consisting of the QB-charger setup and their respective environments. As long as either the quasienergies of the two FBSs are degenerate or the QB-charger coupling is large in the presence of two FBSs, the QB exposed to the dissipative environments returns to its near-ideal cyclic stage. Our result supplies an insightful guideline to realize the QB in practice using Floquet engineering.

quant-ph↗