arXiv subjects

Qing Ai

Publications and source records attributed to Qing Ai.

At least 37 records · Page 2Linked to original sources

arXiv2023

Universal quantum gates by nonadiabatic holonomic evolution for the surface electron

The nonadiabatic holonomic quantum computation based on the geometric phase is robust against the built-in noise and decoherence. In this work, we theoretically propose a scheme to realize nonadiabatic holonomic quantum gates in a surface electron system, which is a promising two-dimensional platform for quantum computation. The holonomic gate is realized by a three-level structure that combines the Rydberg states and spin states via an inhomogeneous magnetic field. After a cyclic evolution, the computation bases pick up different geometric phases and thus perform a geometric gate. Only the electron with spin up experiences the geometric gate, while the electron with spin down is decoupled from the state-selective driving fields. The arbitrary controlled-U gate encoded on the Rydberg states and spin states can then be realized. The fidelity of the output state exceeds 0.99 with experimentally achievable parameters.

quant-ph↗

arXiv2023

Sudden death of entanglement with Hamiltonian ensemble assisted by auxiliary qubits

In this paper, we theoretically propose a method to simulate the longitudinal relaxation of a single qubit by coupling it to an auxiliary qubit. In order to mimic the finite-temperature relaxation, we utilize the Hamiltonian-ensemble approach [Kropf, Gneiting, and Buchleitner, Phys. Rev. X 6, 031023 (2016)] and in each realization the auxiliary qubit possesses a random level spacing. The longitudinal relaxation arises as a consequence of the ensemble average and the interaction between the working qubit and the auxiliary qubit. Furthermore, we apply this approach to investigate the influence of the longitudinal relaxation and the transverse relaxation on the entanglement dynamics of two qubits. It is discovered that the sudden death of the entanglement will occur as long as the longitudinal relaxation is present. The transverse relaxation assists the longitudinal relaxation and thus accelerates the finite-time disentanglement.

quant-ph↗

arXiv2023

Quantum metrology in complex systems and experimental verification by quantum simulation

Quantum metrology based on quantum entanglement and quantum coherence improves the accuracy of measurement. In this paper, we briefly review the schemes of quantum metrology in various complex systems, including non-Markovian noise, correlated noise, quantum critical system. On the other hand, the booming development of quantum information allows us to utilize quantum simulation experiments to test the feasibility of various theoretical schemes and demonstrate the rich physical phenomena in complex systems, such as bound states in one-dimensional coupled cavity arrays, single-photon switches and routers.

quant-ph↗

arXiv2023

Controlled-NOT gate based on the Rydberg states of surface electrons

Due to the long coherence time and efficient manipulation, the surface electron (SE) provides a perfect two-dimensional platform for quantum computation and quantum simulation. In this work, a theoretical scheme to realize the controlled-NOT (CNOT) gate is proposed, where the two-qubit system is encoded on the four-level Rydberg structure of SE. The state transfer is achieved by a three-level structure with an intermediate level. By simultaneously driving the SE with two external electromagnetic fields, the dark state in the electromagnetically induced transparency (EIT) effect is exploited to suppress the population of the most dissipative state and increase the robustness against dissipation. The fidelity of the scheme is 0.9989 with experimentally achievable parameters.

quant-ph↗

arXiv2023

Effects of Disorder On Thouless Pumping In Higher-Order Topological Insulators

We investigate the effects of random onsite disorder on higher-order Thouless pumping of noninteracting fermionic Benalcazar-Bernevig-Hughes (BBH) model. The interplay of disorderinduced topological phase transition and delocalization-localization transition is extensively explored. The higher-order Thouless pumping is characterized by the quantized corner-to-corner charge transport and nonzero Chern number, and the delocalization-localization transition is analyzed by utilizing both inverse participation ratio and energy-level statistics. The results show that the quantized corner-to-corner charge transport is broken in the strong disorder, where the instantaneous bulk energy gap is closed due to effects of disorder. While, although the instantaneous eigenstates are localized, the charge transport remains quantized. This is attributed to delocalized Floquet states caused by the periodic driving. Furthermore, the phase transition from the quantized charge transport to topologically trivial pumping is accompanied by the disorder-induced delocalization-localization transition of Floquet states.

cond-mat.mes-hall↗

arXiv2023

Topological quantum transition driven by charge-phonon coupling in higher-order topological insulators

We investigate a second-order topological quantum transition of a modified Kane-Mele model driven by electron-phonon interaction. The results show that the system parameters of the bare modified Kane-Mele model are renormalized by the electron-phonon interaction. Starting from the second-order topological phase for the bare model, the increasing electron-phonon coupling strength can drive the second-order topological insulator into a semimetal phase. Such a secondorder topological phase transition is characterized by the band-gap closing, discontinuity of averaged ferminoic number and topological invariant.

cond-mat.mes-hall↗

arXiv2023

The effect of static disorder on the center line slope in 2D electronic spectroscopy

Two-dimensional electronic spectroscopy (2DES) is a powerful tool for investigating the dynamics of complex systems. However, analyzing the resulting spectra can be challenging, and thus may require the use of theoretical modeling techniques. The center line slope (CLS) method is one of such approaches, which aims to extract the time correlation function (TCF) from 2DES with minimal error. Since static disorder is widely observed in complex systems, it may be interesting to ask whether the CLS approach still work in the presence of the static disorder. In this paper, the effect of the static disorder on the TCF obtained through the CLS method is investigated. It is found that the steady-state value of the CLS increases monotonically with respect to the static disorder, which suggests that the amplitude of the static disorder can be determined using the CLS in the long-time limit. Additionally, as the static disorder rises, the decay rate of the CLS first decreases to a certain value and remains at this value until the static disorder is sufficiently large. Afterward, the CLS begins to fluctuate significantly and thus results in obtaining the decay rate through the CLS method unreliable. Based on these discoveries, we propose a method to fix the error and obtain the TCF. Our findings may pave the way for obtaining reliable system-bath information by analyzing 2DES in the practical situations.

physics.optics↗

arXiv2022

Criticality-Based Quantum Metrology in the Presence of Decoherence

Quantum metrology aims to use quantum resources to improve the precision of measurement. Quantum criticality has been presented as a novel and efficient resource. Generally, protocols of criticality-based quantum metrology often work without decoherence. In this paper, we address the issue whether the divergent feature of the inverted variance is indeed realizable in the presence of noise when approaching the QPT. Taking the quantum Rabi model (QRM) as an example, we obtain the analytical result for the inverted variance. We show that the inverted variance may be convergent in time due to the noise. When approaching the critical point, the maximum inverted variance demonstrates a power-law increase with the exponent -1.2, of which the absolute value is smaller than that for the noise-free case, i.e., 2. We also observe a power-law dependence of the maximum inverted variance on the relaxation rate and the temperature. Since the precision of the metrology is very sensitive to the noise, as a remedy, we propose performing the squeezing operation on the initial state to improve the precision under decoherence. In addition, we also investigate the criticality-based metrology under the influence of the two-photon relaxation. Contrary to the single-photon relaxation, the quantum dynamics of the inverted variance shows a completely-different behavior. It does not oscillate with the same frequency with respect to the re-scaled time for different dimensionless coupling strengths. Strikingly, although the maximum inverted variance still manifests a power-law dependence on the energy gap, the exponent is positive and depends on the dimensionless coupling strength. This observation implies that the criticality may not enhance but weaken the precision in the presence of two-photon relaxation. It can be well described by the non-linearity introduced by the two-photon relaxation.

quant-ph↗

arXiv2022

Entanglement-Enhanced Quantum Metrology in Colored Noise by Quantum Zeno Effect

In open quantum systems, the precision of metrology inevitably suffers from the noise. {In Markovian open quantum dynamics, the precision can not be improved by using entangled probes although the measurement time is effectively shortened.} However, it was predicted over one decade ago that in a non-Markovian one, the error can be significantly reduced by the quantum Zeno effect (QZE) [Chin, Huelga, and Plenio, Phys. Rev. Lett. \textbf{109}, 233601 (2012)]. In this work, we apply a recently-developed quantum simulation approach to experimentally verify that entangled probes can improve the precision of metrology by the QZE. Up to $n=7$ qubits, we demonstrate that the precision has been improved by a factor of $n^{1/4}$, which is consistent with the theoretical prediction. Our quantum simulation approach may provide an intriguing platform for experimental verification of various quantum metrology schemes.

quant-ph↗

arXiv2022

Sequence-to-Sequence Voice Reconstruction for Silent Speech in a Tonal Language

Silent Speech Decoding (SSD), based on articulatory neuromuscular activities, has become a prevalent task of Brain-Computer Interface (BCI) in recent years. Many works have been devoted to decoding surface electromyography (sEMG) from articulatory neuromuscular activities. However, restoring silent speech in tonal languages such as Mandarin Chinese is still difficult. This paper proposes an optimized Sequence-to-Sequence (Seq2Seq) approach to synthesize voice from the sEMG-based silent speech. We extract duration information to regulate the sEMG-based silent speech using the audio length. Then, we provide a deep-learning model with an encoder-decoder structure and a state-of-art vocoder to generate the audio waveform. Experiments based on six Mandarin Chinese speakers demonstrate that the proposed model can successfully decode silent speech in Mandarin Chinese and achieve a character error rate (CER) of 6.41% on average with human evaluation.

cs.SD↗

arXiv2022

Spontaneous emission modulation in biaxial hyperbolic van der Waals material

As a natural van der Waals crystal, α-MoO3 has excellent in-plane hyperbolic properties and essential nanophotonics applications. However, its actively tunable properties are generally neglected. In this work, we achieved active modulation of spontaneous emission from a single-layer flat plate using the rotation method for the first time. Numerical results and theoretical analysis show that α-MoO3 exhibits good tunability when rotated in the y-z or x-y plane. A modulation factor of more than three orders of magnitude can be obtained at 634 cm-1. However, when the rotation is in the x-z plane, the spontaneous emission of the material exhibits strong angle independence. The theoretical formulation and the physical mechanism analysis explain the above phenomenon well. In addition, for the semi-infinite α-MoO3 flat structure, we give the distribution of the modulation factor of spontaneous emission with wavenumber and rotation angle. Finally, we extended the calculation results from semi-infinite media to finite thickness films. We obtained the general evolution law of the peak angle of the modulation factor with thickness, increasing the modulation factor to about 2000. We believe that the results of this paper can guide the active modulation of spontaneous emission based on anisotropic materials.

physics.optics↗

arXiv2022

Multi-Radical Lipkin-Meshkov-Glick Model for Avian Navigation

The mechanism of avian navigation is an important question for global scientists. One of the most famous candidates is the radical pair mechanism (RPM), which shows that avian navigation is achieved by detecting the amount of products from chemical reactions, which exhibit different properties for singlet and triplet spin states. Based on the theory, we explore the amount of the the singlet recombination product by changing the coupling strength and direction of the magnetic field. The radical pair in our model is coupled with a Lipkin-Meshkov-Glick (LMG) bath, which proposes attractive results at quantum phase transition (QPT) point, especially when the magnetic field is parallel with the original direction of the pair. We find weakest navigation ability in QPT point according to one of our proposing methods. And we find invariant subspace in our Hamiltonian when the magnetic field is vertical to the plane of the radical pair and the bath, which will greatly speed up our calculation. Our results could help the exploration of the design principle of artificial avian navigation.

physics.bio-ph↗

arXiv2022

Global Correlation and Local Information Flows in Controllable Non-Markovian Open Quantum Dynamics

In a fully-controllable experiment platform for studying non-Markovian open quantum dynamics, we show that the non-Markovianity could be investigated from the global and local aspects. By mixing random unitary dynamics, we demonstrate non-Markovian and Markovian open quantum dynamics. From the global point of view, by tuning the base frequency we demonstrate the transition from the Markovianity to the non-Markovianity as measured by the quantum mutual information (QMI). In a Markovian open quantum process, the QMI decays monotonically, while it may rise temporarily in a non-Markovian process. However, under some circumstances, it is not sufficient to globally investigate the non-Markovianity of the open quantum dynamics. As an essential supplement, we further utilize the quantum Fisher information (QFI) flow to locally characterize the non-Markovianity in different channels. We demonstrate that the QMI in combination with the QFI flow are capable of measuring the non-Markovianity for a multi-channel open quantum dynamics.

quant-ph↗

arXiv2021

Optical nonreciprocity in rotating diamond with nitrogen-vacancy center

We theoretically propose a method to realize optical nonreciprocity in rotating nano-diamond with a nitrogen-vacancy (NV) center. Because of the relative motion of the NV center with respect to the propagating fields, the frequencies of the fields are shifted due to the Doppler effect. When the control and probe fields are incident to the NV center from the same direction, the two-photon resonance still holds as the Doppler shifts of the two fields are the same. Thus, due to the electromagnetically-induced transparency (EIT), the probe light can pass through the NV center nearly without absorption. However, when the two fields propagate in opposite directions, the probe light can not effectively pass through the NV center as a result of the breakdown of two-photon resonance.

quant-ph↗

arXiv2021

Quantum metrology with one auxiliary particle in a correlated bath and its quantum simulation

In realistic metrology, entangled probes are more sensitive to noise, especially for a correlated environment. The precision of parameter estimation with entangled probes is even lower than that of the unentangled ones in a correlated environment. In this paper, we propose a measurement scheme with only one auxiliary qubit, which can selectively offset the impact of environmental noise under this situation. We analyse the estimation precision of our scheme and find out that it approaches the Heisenberg limit when prepared in a proper auxiliary state. We further discuss employing auxiliary states to improve the precision of measurement in other environment models such as a partially-correlated environment. In order to verify our scheme, we apply a recently-developed quantum algorithm to simulate the quantum dynamics of our proposal and show that it outperform the other proposals with less resources.

quant-ph↗

arXiv2020

Quantum simulation of clustered photosynthetic light harvesting in a superconducting quantum circuit

We propose a scheme to simulate the exciton energy transfer (EET) of photosynthetic complexes in a quantum superconducting circuit system. Our system is composed of two pairs of superconducting charge qubits coupled to two separated high-Q superconducting transmission line resonators (TLRs) connected by a capacitance. When the frequencies of the qubits are largely detuned with those of the TLRs, we simulate the process of the EET from the first qubit to the fourth qubit. By tuning the couplings between the qubits and the TLRs, and the coupling between the two TLRs, we can modify the effective coupling strengths between the qubits and thus demonstrate the geometric effects on the EET. It is shown that a moderate clustered geometry supports optimal EET by using exciton delocalization and energy matching condition. And the population loss during the EET has been trapped in the two TLRs.

quant-ph↗

arXiv2020

Exact and efficient quantum simulation of open quantum dynamics for various of Hamiltonians and spectral densities

Recently, we have theoretically proposed and experimentally demonstrated an exact and efficient quantum simulation of photosynthetic light harvesting in nuclear magnetic resonance (NMR), cf. B. X. Wang, \textit{et al.} npj Quantum Inf.~\textbf{4}, 52 (2018). In this paper, we apply this approach to simulate the open quantum dynamics in various photosynthetic systems with different Hamiltonians. By numerical simulations, we show that for Drude-Lorentz spectral density the dimerized geometries with strong couplings within the donor and acceptor clusters respectively exhibit significantly-improved efficiency. Based on the optimal geometry, we also demonstrate that the overall energy transfer can be further optimized when the energy gap between the donor and acceptor clusters matches the peak of the spectral density. Moreover, by exploring the quantum dynamics for different types of spectral densities, e.g. Ohmic, sub-Ohmic, and super-Ohmic spectral densities, we show that our approach can be generalized to effectively simulate open quantum dynamics for various Hamiltonians and spectral densities. Because $\log_{2}N$ qubits are required for quantum simulation of an $N$-dimensional quantum system, this quantum simulation approach can greatly reduce the computational complexity compared with popular numerically-exact methods.

quant-ph↗

arXiv2020

Coherent and incoherent theories for photosynthetic energy transfer

There is a remarkable characteristic of photosynthesis in nature, that is, the energy transfer efficiency is close to 100%. Recently, due to the rapid progress made in the experimental techniques, quantum coherent effects have been experimentally demonstrated. Traditionally, the incoherent theories are capable of calculating the energy transfer efficiency, e.g., (generalized) Förster theory and modified Redfield theory. However, in order to describe the quantum coherent effects in photosynthesis, the coherent theories have been developed, such as hierarchical equation of motion, quantum path integral, coherent modified Redfield theory, small-polaron quantum master equation, and general Bloch-Redfield theory in addition to the Redfield theory. Here, we summarize the main points of the above approaches, which might be beneficial to the quantum simulation of quantum dynamics of exciton energy transfer in natural photosynthesis, and shed light on the design of artificial light-harvesting devices.

physics.chem-ph↗