Elimination of Spatial Side-Channel Information for Compact Quantum Key Distribution Senders

For a compact quantum key distribution (QKD) sender for the polarization encoding BB84 protocol, an eavesdropper could take a side-channel attack by measuring the spatial information of photons to infer their polarizations. The possibility of this attack can be reduced by introducing an aperture in the QKD sender, however, the effect of the aperture on the QKD security lacks of quantitative analysis. In this paper, we analyze the mutual information between the actual keys encoded at this QKD sender and the inferred keys at the eavesdropper (Eve), demonstrating the effect of the aperture to eliminate the spatial side-channel information quantitatively. It shows that Eve’s potential on eavesdropping spatial side-channel information is totally dependent on the optical design of the QKD sender, including the source arrangement and the aperture. The height of compact QKD senders with integrated light-emitting diode (LED) arrays could be controlled under several millimeters, showing great potential on applications in portable equipment.

A concise review of Rydberg atom based quantum computation and quantum simulation

Quantum information processing based on Rydberg atoms emerged as a promising direction two decades ago.Recent experimental and theoretical progresses have shined exciting light on this avenue.In this concise review,we will briefly introduce the basics of Rydberg atoms and their recent applications in associated areas of neutral atom quantum computation and simulation.We shall also include related discussions on quantum optics with Rydberg atomic ensembles,which are increasingly used to explore quantum computation and quantum simulation with photons.

Impact of Fiber Dispersion on Performance of Entanglement-Based Dispersive Optics Quantum Key Distribution

Dispersive optics quantum key distribution(DO-QKD)based on energy-time entangled photon pairs is an important QKD scheme.In DO-QKD,the arrival time of photons is used in key generation and security analysis,which would be greatly affected by fiber dispersion.In this work,we establish a theoretical model of the entanglement-based DO-QKD system,considering the protocol,physical processes(such as fiber transmission and single-photon detection),and the analysis of security tests.Based on this theoretical model,we investigate the influence of chromatic dispersion introduced by transmission fibers on the performance of DO-QKD.By analyzing the benefits and costs of dispersion compensation,the system performance under G.652 and G.655 optical fibers are shown,respectively.The results show that dispersion compensation is unnecessary for DO-QKD systems in campus networks and even metro networks.Whereas,it is still required in DO-QKD systems with longer fiber transmission distances.

Broad gain,continuous-wave operation of InP-based quantum cascade laser atλ~11.8μm

We demonstrate a broad gain,continuous-wave(CW)operation InP-based quantum cascade laser(QCL)emitting at 11.8μm with a modified dual-upper-state(DAU)and diagonal transition active region design.A 3 mm cavity length,16.5μm average ridge wide QCL with high-reflection(HR)coatings demonstrates a maximum peak power of 1.07 W at 283 K and CW output power of 60 m W at 293 K.The device also shows a broad and dual-frequency lasing spectrum in pulsed mode and a maximum average power of 258.6 mW at 283 K.Moreover,the full width at half maximum(FWHM)of the electroluminescent spectrum measured at subthreshold current is 2.37μm,which indicates a broad gain spectrum of the materials.The tuning range of 1.38μm is obtained by a grating-coupled external cavity(EC)Littrow configuration,which is beneficial for gas detection.

The application of quantum coherence as a resource

Quantum coherence is a basic concept in quantum mechanics, representing one of the most fundamental characteristics that distinguishes quantum mechanics from classical physics. Quantum coherence is the basis for multi-particle interference and quantum entanglement. It is also the essential ingredient for various physical phenomena in quantum optics, quantum information, etc. In recent years, with the proposal of a quantum coherence measurement scheme based on a resource theory framework, quantum coherence as a quantum resource has been extensively investigated. This article reviews the resource theories of quantum coherence and introduces the important applications of quantum coherence in quantum computing,quantum information, and interdisciplinary fields, particularly in quantum thermodynamics and quantum biology. Quantum coherence and its applications are still being explored and developed. We hope this review can provide inspiration for relevant research.

In Situ Epitaxy of Pure Phase Ultra-Thin InAs-Al Nanowires for Quantum Devices

We demonstrate the in situ growth of ultra-thin InA s nanowires with an epitaxial Al film by molecular-beam epitaxy.Our InAs nanowire diameter(~30 nm)is much thinner than before(~100 nm).The ultra-thin InAs nanowires are pure phase crystals for various different growth directions.Transmission electron microscopy confirms an atomically abrupt and uniform interface between the Al shell and the InAs wire.Quantum transport study on these devices resolves a hard induced superconducting gap and 2 e-periodic Coulomb blockade at zero magnetic field,a necessary step for future Majorana experiments.By reducing wire diameter,our work presents a promising route for reaching fewer sub-band regime in Major ana nanowire devices.

Simulation of Projective Non-Abelian Anyons for Quantum Computation

Fundamental particles in nature can be classified as bosons or fermions,which satisfy their correspondent statistics.However,quasiparticles of condensed matter physics may be neither bosons nor fermions,but can be named as anyons satisfying a generalized statistics.These anyons can be related with topological phases of matter.Interestingly,anyons can be used to encode qubits to perform quantum computations with specific advantages in which the corresponding qubits are naturally fault tolerant due to topological protection.[1,2]This approach is called topological quantum computation.However,its implementation based on natural systems still seems far from realization.

Realization of arbitrary two-qubit quantum gates based on chiral Majorana fermions

Quantum computers are in hot-spot with the potential to handle more complex problems than classical computers can.Realizing the quantum computation requires the universal quantum gate set {T,H,CNOT} so as to perform any unitary transformation with arbitrary accuracy.Here we first briefly review the Majorana fermions and then propose the realization of arbitrary two-qubit quantum gates based on chiral Majorana fermions.Elementary cells consist of a quantum anomalous Hall insulator surrounded by a topological superconductor with electric gates and quantum-dot structures,which enable the braiding operation and the partial exchange operation.After defining a qubit by four chiral Majorana fermions,the singlequbit T and H quantum gates are realized via one partial exchange operation and three braiding operations,respectively.The entangled CNOT quantum gate is performed by braiding six chiral Majorana fermions.Besides,we design a powerful device with which arbitrary two-qubit quantum gates can be realized and take the quantum Fourier transform as an example to show that several quantum operations can be performed with this space-limited device.Thus,our proposal could inspire further utilization of mobile chiral Majorana edge states for faster quantum computation.

Exciton emission dynamics in single InAs/GaAs quantum dots due to the existence of plasmon-field-induced metastable states in the wetting layer

A very long lifetime exciton emission with non-single exponential decay characteristics has been reported for single InA-s/GaAs quantum dot(QD)samples,in which there exists a long-lived metastable state in the wetting layer(WL)through radiative field coupling between the exciton emissions in the WL and the dipole field of metal islands.In this article we have proposed a new three-level model to simulate the exciton emission decay curve.In this model,assuming that the excitons in a metastable state will diffuse and be trapped by QDs,and then emit fluorescence in QDs,a stretchedlike exponential decay formula is derived as I(t)=At^(β−1)e^(−(rt)^(β)),which can describe well the long lifetime decay curve with an analytical expression of average lifetime(τ)=1/rГ(1/β+1),where G is the Gamma function.Furthermore,based on the proposed three-level model,an expression of the second-order auto-correlation function g^(2)(t)which can fit the measured g^(2)(t)curve well,is also obtained.

Evolution of Superconducting-Transition Temperature with Superfluid Density and Conductivity in Pressurized Cuprate Superconductors

What factors fundamentally determine the value of superconducting transition temperature Tc in high temperature superconductors has been the subject of intense debate.Following the establishment of an empirical law known as Homes'law,there is a growing consensus in the community that the Tc value of the cuprate superconductors is closely linked to the superfluid density(ρ_(s))of its ground state and the conductivity(σ)of its normal state.However,all the data supporting this empirical law(ρ_(s)=AσT_(c))have been obtained from the ambientpressure superconductors.In this study,we present the first high-pressure results about the connection of the quantities of ρ_(s) and σ with T_(c),through the studies on the Bi_(1.74)Pb_(0.38)Sr_(1.88)CuO_(6+δ)and Bi_(2)Sr_(2)CaCu_(2)O_(8+δ),in which the value of their high-pressure resistivity(ρ=1/σ)is achieved by adopting our newly established method,while the quantity ofρs is extracted using Homes'law.We highlight that the Tc values are strongly linked to the joint response factors of magnetic field and electric field,i.e.,ρ_(s) and σ,respectively,implying that the physics determining T_(c) is governed by the intrinsic electromagnetic fields of the system.

Quantum computation and simulation with vibrational modes of trapped ions

Vibrational degrees of freedom in trapped-ion systems have recently been gaining attention as a quantum resource,beyond the role as a mediator for entangling quantum operations on internal degrees of freedom,because of the large available Hilbert space.The vibrational modes can be represented as quantum harmonic oscillators and thus offer a Hilbert space with infinite dimensions.Here we review recent theoretical and experimental progress in the coherent manipulation of the vibrational modes,including bosonic encoding schemes in quantum information,reliable and efficient measurement techniques,and quantum operations that allow various quantum simulations and quantum computation algorithms.We describe experiments using the vibrational modes,including the preparation of non-classical states,molecular vibronic sampling,and applications in quantum thermodynamics.We finally discuss the potential prospects and challenges of trapped-ion vibrational-mode quantum information processing.

Quantum simulation and quantum computation of noisy-intermediate scale

In the past years, great progresses have been made on quantum computation and quantum simulation. Increasing the number of qubits in the quantum processors is expected to be one of the main motivations in the next years, while noises in manipulation of quantum states may still be inevitable even the precision will improve. For research in this direction, it is necessary to review the available results about noisy multiqubit quantum computation and quantum simulation. The review focuses on multiqubit state generations, quantum computational advantage, and simulating physics of quantum many-body systems. Perspectives of near term noisy intermediate-quantum processors will be discussed.

Phonon-assisted upconversion photoluminescence of quantum emitters

Quantum emitters are widely used in quantum networks,quantum information processing,and quantum sensing due to their excellent optical properties.Compared with Stokes excitation,quantum emitters under anti-Stokes excitation exhibit better performance.In addition to laser cooling and nanoscale thermometry,anti-Stokes excitation can improve the coherence of single-photon sources for advanced quantum technologies.In this review,we follow the recent advances in phononassisted upconversion photoluminescence of quantum emitters and discuss the upconversion mechanisms,applications,and prospects for quantum emitters with anti-Stokes excitation.

Observation of source/drain bias-controlled quantum transport spectrum in junctionless silicon nanowire transistor

We investigate the influence of source and drain bias voltages(V_(DS))on the quantum sub-band transport spectrum in the 10-nm width N-typed junctionless nanowire transistor at the low temperature of 6 K.We demonstrate that the transverse electric field introduced from V_(DS) has a minor influence on the threshold voltage of the device.The transverse electric field plays the role of amplifying the gate restriction effect of the channel.The one-dimensional(1D)-band dominated transport is demonstrated to be modulated by V_(DS) in the saturation region and the linear region,with the sub-band energy levels in the channel(E_(channel))intersecting with Fermi levels of the source(E_(fS))and the drain(E_(fD))in turn as V_(g) increases.The turning points from the linear region to the saturation region shift to higher gate voltages with V_(DS) increase because the higher Fermi energy levels of the channel required to meet the situation of E_(fD)=E_(channel).We also find that the bias electric field has the effect to accelerate the thermally activated electrons in the channel,equivalent to the effect of thermal temperature on the increase of electron energy.Our work provides a detailed description of the bias-modulated quantum electronic properties,which will give a more comprehensive understanding of transport behavior in nanoscale devices.

Quantum light source devices of In(Ga)As semiconductor self-assembled quantum dots

A brief introduction of semiconductor self-assembled quantum dots (QDs) applied in single-photon sources is given. Single QDs in confined quantum optical microcavity systems are reviewed along with their optical properties and coupling characteristics. Subsequently, the recent progresses in In(Ga)As QDs systems are summarized including the preparation of quantum light sources, multiple methods for embedding single QDs into different microcavities and the scalability of single-photon emitting wavelength. Particularly, several In(Ga)As QD single-photon devices are surveyed including In(Ga)As QDs coupling with nanowires, InAs QDs coupling with distributed Bragg reflection microcavity and the In(Ga)As QDs coupling with micropillar microcavities. Furthermore, applications in the field of single QDs technology are illustrated, such as the entangled photon emission by spontaneous parametric down conversion, the single-photon quantum storage, the chip preparation of single-photon sources as well as the single-photon resonance-fluorescence measurements.

High-temperature continuous-wave operation of 1310 nm InAs/GaAs quantum dot lasers

Here we report 1.3μm electrical injection lasers based on InAs/GaAs quantum dots(QDs)grown on a GaAs substrate,which can steadily work at 110-℃without visible degradation.The QD structure is designed by applying the Stranski-Krastanow growth mode in solid source molecular beam epitaxy.The density of InAs QDs in the active region is increased from 3.8×10^(10)cm^(-2)to 5.9×10^(10)cm^(-2).As regards laser performance,the maximum output power of devices with lowdensity QDs as the active region is 65 m W at room temperature,and that of devices with the high-density QDs is 103 mW.Meanwhile the output power of high-density devices is 131 mW under an injection current of 4 A at 110-℃.

Variational quantum simulation of thermal statistical states on a superconducting quantum processer

Quantum computers promise to solve finite-temperature properties of quantum many-body systems,which is generally challenging for classical computers due to high computational complexities.Here,we report experimental preparations of Gibbs states and excited states of Heisenberg X X and X X Z models by using a 5-qubit programmable superconducting processor.In the experiments,we apply a hybrid quantum–classical algorithm to generate finite temperature states with classical probability models and variational quantum circuits.We reveal that the Hamiltonians can be fully diagonalized with optimized quantum circuits,which enable us to prepare excited states at arbitrary energy density.We demonstrate that the approach has a self-verifying feature and can estimate fundamental thermal observables with a small statistical error.Based on numerical results,we further show that the time complexity of our approach scales polynomially in the number of qubits,revealing its potential in solving large-scale problems.

Progress and realization platforms of dynamic topological photonics

Dynamic topological photonics is a novel research field, combining the time-domain optics and topological physics.In this review, the recent progress and realization platforms of dynamic topological photonics have been well introduced.The definition, measurement methods and the evolution process of the dynamic topological photonics are demonstrated to better understand the physical diagram. This review is meant to bring the readers a different perspective on topological photonics, grasp the advanced progress of dynamic topology, and inspire ideas about future prospects.

Phase-locked single-mode terahertz quantum cascade lasers array

We demonstrated a scheme of phase-locked terahertz quantum cascade lasers(THz QCLs)array,with a single-mode pulse power of 108 mW at 13 K.The device utilizes a Talbot cavity to achieve phase locking among five ridge lasers with first-order buried distributed feedback(DFB)grating,resulting in nearly five times amplification of the single-mode power.Due to the optimum length of Talbot cavity depends on wavelength,the combination of Talbot cavity with the DFB grating leads to better power amplification than the combination with multimode Fabry-Perot(F-P)cavities.The Talbot cavity facet reflects light back to the ridge array direction and achieves self-imaging in the array,enabling phase-locked operation of ridges.We set the spacing between adjacent elements to be 220μm,much larger than the free-space wavelength,ensuring the operation of the fundamental supermode throughout the laser's dynamic range and obtaining a high-brightness far-field distribution.This scheme provides a new approach for enhancing the single-mode power of THz QCLs.

Generalized Quantum Measurement in Spin-Correlated Hyperon-Antihyperon Decays

The rapid developments of quantum information science(QIS)have opened up new avenues for exploring fundamental physics.Quantum nonlocality,a key aspect for distinguishing quantum information from classical one,has undergone extensive examinations in particles’decays through the violation of Bell-type inequalities.Despite these advancements,a comprehensive framework based on quantum information theory for particle interaction is still lacking.Trying to close this gap,we introduce a generalized quantum measurement description for decay processes of spin-1/2 hyperons.We validate this approach by aligning it with established theoretical calculations and apply it to the joint decay of ΛΛ pairs.We employ quantum simulation to observe the violation of Clauser–Horne–Shimony–Holt inequalities in η_(c)/χ_(c0)→ΛΛˉprocesses.Our generalized measurement description is adaptable and can be extended to a variety of high energy processes,including decays of vector mesons,J/ψ,ψ(2S)→ΛΛ,in the Beijing Spectrometer Ⅲ(BESⅢ)experiment at the Beijing Electron Positron Collider(BEPC).The methodology developed in this study can be applied to quantum correlation and information processing in fundamental interactions.