arXiv subjects

Jun-Hong An

Publications and source records attributed to Jun-Hong An.

At least 37 records · Page 2Linked to original sources

arXiv2025

Mechanical Squeezed-Fock Qubit: Towards Quantum Weak-Force Sensing

Mechanical qubits offer unique advantages over other qubit platforms, primarily in terms of coherence time and possibilities for enhanced sensing applications, but their potential is constrained by the inherently weak nonlinearities and small anharmonicity of nanomechanical resonators. We propose to overcome this shortcoming by using squeezed Fock states of phonons in a parametrically driven nonlinear mechanical oscillator. We find that, under two-phonon driving, squeezed Fock states become eigenstates of a Kerr-nonlinear mechanical oscillator, featuring an energy spectrum with exponentially enhanced and tunable anharmonicity, such that the transitions to higher energy states are exponentially suppressed. This enables us to encode the mechanical qubit within the ground and first excited squeezed Fock states of the driven mechanical oscillator. This kind of mechanical qubit is termed mechanical squeezed-Fock qubit. We also show that our mechanical qubit can serve as a quantum sensor for weak forces, with its resulting sensitivity increased by at least one order of magnitude over that of traditional mechanical qubits. The proposed mechanical squeezed-Fock qubit provides a powerful quantum phonon platform for quantum sensing and information processing.

quant-ph↗

arXiv2025

Quantum surface effects on quantum emitters coupled to surface plasmon polariton

As an ideal platform for exploring strong quantized light-matter interactions, surface plasmon polariton (SPP) has inspired many applications in quantum technologies. Recent experiments discovered that quantum surface effects (QSEs) of the metal, including nonlocal optical response, electron spill-out, and Landau damping, invalidate the classical electromagnetic theory and contribute additional loss sources to the SPP in the nanoscale. This hinders its applications. Going beyond the widely used classical local response approximation, we use the Feibelman $d$-parameter method to investigate the QSE-modified non-Markovian dynamics of quantum emitters (QEs) coupled to a SPP in a planar metal-dielectric nanostructure. A mechanism to overcome the dissipation of the QEs caused by the lossy SPP with the QSEs is discovered. We find that, as long as the QE-SPP bound states are formed, a dissipationless entanglement among the far-separated QEs is created. Compared with the local-response approximate results, the QSEs play a constructive role in establishing such a coherent correlation. The result lays a foundation for understanding the light-matter interactions in absorptive media and paves the way for the application of SPP in quantum network.

quant-ph↗

arXiv2025

Topological semimetal with coexisting nodal points and nodal lines

Featuring exotic quantum transport and surface states, topological semimetals can be classified into nodal-point, nodal-line, and nodal-surface semimetals according to the degeneracy and dimensionality of their nodes. However, a topological semimetal that possesses both nodal points and nodal lines is rarely reported. Here, we propose a scheme to construct this type of topological semimetal, which simultaneously exhibits hinge Fermi arcs and drumhead surface states. Then, by applying periodic driving on the system, we find a hybrid-order topological semimetal with nodal points and rich nodal-line structures and its conversion into a first-order topological semimetal, which are absent in a static system. Our results enrich the family of topological semimetals, and establish a foundation for further exploration of their potential applications.

cond-mat.mes-hall↗

arXiv2025

Self-Discharging Mitigated Quantum Battery

As a quantum thermodynamic device that utilizes quantum systems for energy storage and delivery, the quantum battery (QB) is expected to offer revolutionary advantages in terms of increasing the charging power and the extractable work by using quantum resources. However, the ubiquitous decoherence in the microscopic world inevitably forces the QB to spontaneously lose its stored energy. This is called the self-discharging of the QB and severely limits its realization. We propose a QB scheme based on the nitrogen-vacancy center in diamond, where the electronic spin serves as the QB. Inspired by our finding that the coherent ergotropy decays more slowly than the incoherent ergotropy, we reveal a mechanism to enhance the inherent robustness of the QB to the self-discharging by improving the ratio of coherent ergotropy to total ergotropy. The unique hyperfine interaction between the electron and the native $^{14}$N nucleus in our scheme allows one to coherently optimize this ratio. Mitigating the self-discharging and optimizing the extractable work simultaneously, our results pave the way for the practical realization of the QB.

quant-ph↗

arXiv2025

Breakdown of boundary criticality and exotic topological semimetals in $\mathcal{P}\mathcal{T}$-invariant systems

It was recently found that, going beyond the tendfold Altland-Zirnbauer symmetry classes and violating the bulk-boundary correspondence of the usual topological phases, PT-invariant systems support a real Chern insulator with the so-called boundary criticality, which forbids the transition between different orders of topological phases accompanied by the closing and reopening of the bulk-band gap. Here, we fnd that the periodic driving can break the boundary criticality of a PT-invariant system. Setting free from the the boundary criticality, diverse first- and second-order topological phases absent in the static case are found in both the zero and Pi/T modes. The application of our result in the three-dimensional PT-invariant system permits us to discover exotic second-order Dirac and nodal-line semimetals with coexisting surface and hinge Fermi arcs. Enriching the family of the topological phases in PT-invariant systems, our result provides us a useful way to explore novel topological phases.

cond-mat.mes-hall↗

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.

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arXiv2024

Unveiling Higher-Order Topology via Polarized Topological Charges

Higher-order topological phases (HOTPs) host exotic topological states that go beyond the traditional bulk-boundary correspondence. Up to now, there is still a lack of experimentally measurable momentum-space topological characterization for the HOTPs, which is not conducive to revealing the essential properties of these topological states and also restricts their detection in quantum simulation systems. Here, we propose a concept of polarized topological charges to characterize chiral-symmetric HOTPs in momentum space, which further facilitates a feasible experimental scheme to detect the HOTPs in $^{87}$Rb cold atomic system. Remarkably, our characterization theory not only shows that the second-order (third-order) topological phases are determined by a quarter (negative eighth) of the total polarized topological charges, but also reveals that the higher-order topological phase transitions are identified by the creation or annihilation of polarized topological charges. Particularly, these polarized topological charges can be measured by pseudospin structures of the systems. Due to theoretical simplicity and observational intuitiveness, this work shall advance the broad studies of the HOTPs in both theory and experiment.

cond-mat.mes-hall↗

arXiv2024

Generalized Quantum Fluctuation Theorem for Energy Exchange

The nonequilibrium fluctuation relation is a cornerstone of quantum thermodynamics. It is widely believed that the system-bath heat exchange obeys the famous Jarzynski-Wójcik fluctuation theorem. However, this theorem is established in the Born-Markovian approximation under the weak-coupling condition. Via studying the energy exchange between a harmonic oscillator and its coupled bath in the non-Markovian dynamics, we establish a generalized quantum fluctuation theorem for energy exchange being valid for arbitrary coupling strength. The Jarzynski-Wójcik fluctuation theorem is recovered in the weak-coupling limit. We also find the average energy exchange exhibits rich nonequilibrium characteristics when different numbers of system-bath bound states are formed, which suggests a useful way to control the quantum heat. Deepening our understanding of the fluctuation relation in quantum thermodynamics, our result lays the foundation to design high-efficiency quantum heat engines.

quant-ph↗

arXiv2024

Noise mitigation in quantum teleportation

Permitting the transmission of unknown quantum states over long distances by using entanglement, quantum teleportation serves as an important building block for many quantum technologies. However, in the noisy intermediate-scale quantum era, the practical realization of quantum teleportation is inevitably challenged by the noise-induced decoherence. We here propose a noise-mitigation mechanism applicable in both the discrete- and continuous-variable quantum teleportation schemes. Via investigating the non-Markovian decoherence dynamics of the two types of quantum teleportation schemes, we find that, as long as a bound state is formed in the energy spectrum of the total system consisting of the involved subsystems and their respective reservoirs, the quantum superiority of the fidelity is persistently recovered. Supplying an insightful understanding of the noise-mitigation protocols, our result paves the way to the practical realization of noise-tolerant quantum teleportation.

quant-ph↗

arXiv2024

Majorana modes in trapped-ion system and their Floquet engineering

Obeying non-Abelian statistics, Majorana fermions holds a promise to implement fault-tolerant quantum computing. It was found that Majorana fermions can be simulated by the zero-energy excitation in a nanowire with strong spin-orbit coupling interacting with an $s$-wave superconductor under a magnetic field. However, the signal of Majorana fermion in that system is obscured by the disorder in the nanowire and the confinement potential at the wire end. Thus, more controllable platforms are desired to simulate Majorana fermions. We here propose an alternative scheme to simulate the Majorana fermions in a trapped-ion system. Our dimerized-ion configuration permits us to generate the Majorana modes not only at zero energy but also at the nonzero ones, which enlarge the family of Majorana modes and supply another qubit carrier for quantum computing. We also investigate the controllability of the Majorana modes by Floquet engineering. It is found that a widely tunable number of Majorana modes are created on demand by applying a periodic driving on the trapped-ion system. Enriching the platforms for simulating Majorana fermions, our result would open another avenue for realizing fault-tolerant quantum computing.

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↗

arXiv2024

Remote Charging and Degradation Suppression for the Quantum Battery

The quantum battery (QB) makes use of quantum effects to store and supply energy, which may outperform its classical counterpart. However, there are two challenges in this field. One is that the environment-induced decoherence causes the energy loss and aging of the QB, the other is that the decreasing of the charger-QB coupling strength with increasing their distance makes the charging of the QB become inefficient. Here, we propose a QB scheme to realize a remote charging via coupling the QB and the charger to a rectangular hollow metal waveguide. It is found that an ideal charging is realized as long as two bound states are formed in the energy spectrum of the total system consisting of the QB, the charger, and the electromagnetic environment in the waveguide. Using the constructive role of the decoherence, our QB is immune to the aging. Additionally, without resorting to the direct charger-QB interaction, our scheme works in a way of long-range and wireless-like charging. Effectively overcoming the two challenges, our result supplies an insightful guideline to the practical realization of the QB by reservoir engineering.

quant-ph↗

arXiv2024

Quantum-state engineering in cavity magnomechanics formed by two-dimensional magnetic materials

Cavity magnomechanics has become an ideal platform to explore macroscopic quantum effects. Bringing together magnons, phonons, and photons in a system, it opens many opportunities for quantum technologies. It was conventionally realized by an yttrium iron garnet, which exhibits a parametric magnon-phonon coupling $\hat{m}^†\hat{m}(\hat{b}^†+\hat{b})$, with $\hat{m}$ and $\hat{b}$ being the magnon and phonon modes. Inspired by the recent realization of two-dimensional (2D) magnets, we propose a cavity magnomechanical system using a 2D magnetic material with both optical and magnetic drivings. It features the coexisting photon-phonon radiation-pressure coupling and quadratic magnon-phonon coupling $\hat{m}^†\hat{m}(\hat{b}^†+\hat{b})^2$ induced by the magnetostrictive interaction. A stable squeezing of the phonon and bi- and tri-partite entanglements among the three modes are generated in the regimes with a suppressed phonon number. Compared with previous schemes, ours does not require any extra nonlinear interaction and reservoir engineering and is robust against the thermal fluctuation. Enriching the realization of cavity magnomechanics, our system exhibits its superiority in quantum-state engineering due to the versatile interactions enabled by its 2D feature.

quant-ph↗

arXiv2023

Engineering rich two-dimensional higher-order topological phases by flux and periodic driving

Nodal-line semimetals are commonly believed to exist in $\mathcal{PT}$ symmetric or mirror-rotation symmetric systems. Here, we find a flux-induced parameter-dimensional second-order nodal-line semimetal (SONLS) in a two-dimensional system without $\mathcal{PT}$ and mirror-rotation symmetries. It has coexisting hinge Fermi arcs and drumhead surface states. Meanwhile, we discover a flux-induced second-order topological insulator (SOTI). We then propose a Floquet engineering scheme to create exotic parameter-dimensional hybrid-order nodal-line semimetals with abundant nodal-line structures and widely tunable numbers of corner states in a SONLS and SOTI, respectively. Our results break the perception of SONLSs and supply a convenient way to artificially synthesize exotic topological phases by periodic driving.

cond-mat.mes-hall↗

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

Kerr nonlinearity induced strong spin-magnon coupling

One pillar of quantum magnonics is the exploration of the utilization of the mediation role of magnons in different platforms to develop quantum technologies. The efficient coupling between magnons and various quantum entities is a prerequisite. Here, we propose a scheme to enhance the spin-magnon coupling by the magnonic Kerr nonlinearity in a YIG sphere. We find that the Kerr-enhanced spin-magnon coupling invalidates the widely used single-Kittel-mode approximation to magnons. It is revealed that the spin decoherence induced by the multimode magnons in the strong-coupling regime becomes not severe, but suppressed, manifesting as either population trapping or persistent Rabi-like oscillation. This anomalous effect is because the spin changes to be so hybridized with the magnons that one or two bound states are formed between them. Enriching the spin-magnon coupling physics, the result supplies a guideline to control the spin-magnon interface.

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↗

arXiv2023

Quantum speed limit from a quantum-state-diffusion method

Characterizing the most efficient evolution, the quantum speed limit (QSL) plays a significant role in quantum technology. How to generalize the well-established QSL from closed systems to open systems has attracted much attention. In contrast to the previous schemes to derive the QSL from the reduced dynamics of open system, we propose a QSL bound from the point of view of the total system consisting of the open system and its environment using a quantum-state-diffusion method. The application of our scheme to a two-level system reveals that the system possesses an infinite speedup capacity in the noiseless case, which is destroyed by the environment under the Born-Markovian approximation. It is interesting to find that the capacity in the noiseless case is recovered in the non-Markovian dynamics as long as a bound state is formed in the energy spectrum of the total system. Enriching the characterization schemes of the QSL, our result provides an efficient way to control the QSL of open systems.

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