Quantum mechanical photoncount formula derived by entangled state representation

By introducing the thermo entangled state representation, we derive four new photocount distribution formulas for a given light field density operator. It is shown that these new formulas, which are convenient to calculate the photocount, can be expressed as integrations over a Laguree Gaussian function with a characteristic function, Wigner function, Q-function and P-function, respectively.

Continuous-Variable Quantum Computation in Circuit QED

Quantum computation (QC) offers the promise of enhanced computational capabilities and drastic accelerations in solving complex tasks such as quantum chemistry^([1,2])and prime factorization.^([3])Various physical implementations for practical QC are being pursued across the academic and industrial research initiatives.Exemplary ones include trapped ions,^([4])nuclear spin,^([5]).

Universal Quantum Cloning Machine in Circuit Quantum Electrodynamics

我们为认识到与超导的量干扰克隆机器(UQCM ) 的 1 2 通用的量建议一个计划在电路量 electrodynamics (电路证完) 的设备(枪乌) qubits。在这个计划，以便实现 UQCM，我们需要仅仅在枪乌 qubits 和拉曼转变上分阶段执行移动门操作。我们需要的洞数字仅仅是一个。因此我们的计划简单并且在试验性的实现有优点。而且，洞和 SQUID qubits 是几乎激动的，因此 decoherence 能被忽视。

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.

Ultradilute self-bound quantum droplets in Bose–Bose mixtures at finite temperature

We theoretically investigate the finite-temperature structure and collective excitations of a self-bound ultradilute Bose droplet in a flat space realized in a binary Bose mixture with attractive inter-species interactions on the verge of meanfield collapse. As the droplet formation relies critically on the repulsive force provided by Lee–Huang–Yang quantum fluctuations, which can be easily compensated by thermal fluctuations, we find a significant temperature effect in the density distribution and collective excitation spectrum of the Bose droplet. A finite-temperature phase diagram as a function of the number of particles is determined. We show that the critical number of particles at the droplet-to-gas transition increases dramatically with increasing temperature. Towards the bulk threshold temperature for thermally destabilizing an infinitely large droplet, we find that the excitation-forbidden, self-evaporation region in the excitation spectrum, predicted earlier by Petrov using a zero-temperature theory, shrinks and eventually disappears. All the collective excitations, including both surface modes and compressional bulk modes, become softened at the droplet-to-gas transition. The predicted temperature effects of a self-bound Bose droplet in this work could be difficult to measure experimentally due to the lack of efficient thermometry at low temperatures. However, these effects may already present in the current cold-atom experiments.

Measurable Dielectric Permittivity Range for TE and TM Modes in a Shielded Dielectric Resonator

Dielectric resonator methods constitute one of the most useful techniques for the measurement of electromagnetic material properties in the microwave frequency range. Several geometric configurations are used for this purpose and, in the present paper, we consider the case of a dielectric rod enclosed in a cylindrical metallic enclosure. To carry out dielectric measurements in this system it is necessary to know the highest permittivity constant value for which the resonance condition still can be attained into the cavity. Using an approach based on magnetic and electric Hertzian potentials we have derived the set of TE and TM modes for the relevant geometry described and, then we have calculated the valid dielectric permittivity constant range of measurements for low-loss materials in a cylindrical cavity using a simple resonance frequency condition. Finally, we present a simple application of this method in order to determine the dielectric permittivity constant of heavy oil with 11 API.

Six-State Symmetric Quantum Key Distribution Protocol

We propose and demonstrate an optical implementation of a quantum key distribution protocol, which uses three-non-orthogonal states and six states in total. The proposed scheme improves the protocol that is proposed by Phoenix, Barnett and Chefles [J. Mod. Opt. 47, 507 (2000)]. An additional feature, which we introduce in our scheme, is that we add another detection set;where each detection set has three non-orthogonal states. The inclusion of an additional detection set leads to improved symmetry, increased eavesdropper detection and higher security margin for our protocol.

Intercept-resend attack on six-state quantum key distribution over collective-rotation noise channels

We investigate the effect of collective-rotation noise on the security of the six-state quantum key distribution. We study the case where the eavesdropper, Eve, performs an intercept-resend attack on the quantum communication between Alice, the sender, and Bob, the receiver. We first derive the collective-rotation noise model for the six-state protocol and then parameterize the mutual information between Alice and Eve. We then derive quantum bit error rate for three interceptresend attack scenarios. We observe that the six-state protocol is robust against intercept-resend attacks on collective rotation noise channels when the rotation angle is kept within certain bounds.

Recent progress in quantum photonic chips for quantum communication and internet

Recent years have witnessed significant progress in quantum communication and quantum internet with the emerging quantum photonic chips,whose characteristics of scalability,stability,and low cost,flourish and open up new possibilities in miniaturized footprints.Here,we provide an overview of the advances in quantum photonic chips for quantum communication,beginning with a summary of the prevalent photonic integrated fabrication platforms and key components for integrated quantum communication systems.We then discuss a range of quantum communication applications,such as quantum key distribution and quantum teleportation.Finally,the review culminates with a perspective on challenges towards high-performance chip-based quantum communication,as well as a glimpse into future opportunities for integrated quantum networks.

Quantum dense coding with gravitational cat states

A protocol of quantum dense coding with gravitational cat states is proposed.We explore the effects of temperature and system parameters on dense coding capacity and provide an efficient strategy to preserve the quantum advantage of dense coding for these states.Our results may open new opportunities for secure communication and insights into the fundamental nature of gravity in the context of quantum information processing.

Experimental symmetric private information retrieval with measurement-device-independent quantum network

Secure information retrieval is an essential task in today's highly digitised society.In some applications,it may be necessary that user query's privacy and database content's security are enforced.For these settings,symmetric private information retrieval(SPIR)could be employed,but its implementation is known to be demanding,requiring a private key-exchange network as the base layer.Here,we report for the first time a realisation of provably-secure SPIR supported by a quantum-secure key-exchange network.The SPIR scheme looks at biometric security,offering secure retrieval of 582-byte fingerprint files from a database with 800 entries.Our experimental results clearly demonstrate the feasibility of SPIR with quantum secure communications,thereby opening up new possibilities in secure distributed data storage and cloud computinq over the future Quantum Internet.

Proposed Entanglement Swapping in Continuous Variable Systems via Braiding

We study entanglement swapping in continuous variable systems by using braiding transformations.It isfound that entanglement swapping in two-mode squeezed vacuum states and squeezed coherent states can be realizedbased on the braiding operators.

Stark-Chirped Rapid Adiabatic Passage in Presence of Dissipation for Quantum Computation

Stark-chirped rapid adiabatic passage(SCRAP) is an important technique used for coherent quantum controls. In this paper we investigate how the practically-existing dissipation of the system influences on the efficiency of the passage, and thus the fidelities of the SCRAP-based quantum gates. With flux-biased Josephson qubits as a specifical example, our results show clearly that the efficiency of the logic gates implemented by SCRAP are robust against the weak dissipation. The influence due to the non-adiabtic transitions between the adiabatic passages is comparatively significantly small. Therefore, the SCRAP-based logic gates should be feasible for the realistic physical systems with noises.

Demonstrating an additional law of relativistic velocities based on squeezed light

The special relativity is the foundation for many branches of modern physics, of which the theoretical results are far beyond our daily experience and hard to realized in kinematic experiments. However, its outcomes could be demonstrated by making use of the convenient substitute, i.e., the squeezed light in the present paper. The squeezed light is very important in the field of quantum optics, and the corresponding transformation can be regarded as the coherent state of SU（1,1）. In this paper, the connection between the squeezed operator and the Lorentz boost is built under certain conditions. Furthermore, the additional law of relativistic velocities and the angle of the Wigner rotation are deduced as well.

Energy Variance in Decoherence

We study the effect of the initial-state energy variance to the short-time behavior of the Loschmidt echo(LE) in a purely dephasing model. We find that the short-time LE behaves as a Gaussian function with the width determined by the initial-state energy variance of the interaction Hamiltonian, while it is a quartic decaying function with the width determined by the initial-state energy variance of the commutator between the interaction Hamiltonian and the environmental Hamiltonian when the initial state is an eigenstate of the interaction Hamiltonian.Furthermore, the Gaussian envelope in the temporal evolution of LE in strong coupling regime is determined by the inband variance. We will also verify the above conclusion in the XY spin model(as environment).

Effects of Interactions and Temperature in Disordered Ultra-Cold Bose Gases

We simulate ultra-cold interacting bosons in quasi-one-dimensional, incommensurate optical lattices. In the tight-binding limit, these lattices have pseudo-random on-site energies and thus can potentially lead to Anderson localization. We use the Hartree-Fock-Bogoliubov formalism in the Bose-Hubbard model to explore the parameter regimes that lead to exponential localization of the ground state in a 3-colour optical lattice and investigate the role of repulsive interactions, harmonic confinement and finite temperature.

基于里德堡原子电场传感的计量、通信以及混合量子系统

Rydberg atoms-based electric field sensing has developed rapidly over the past decade.A variety of theoretical proposals and experiment configurations are suggested and realized to improve the measurement metrics,such as intensity sensitivity,bandwidth,phase,and accuracy.The Stark effect and electromagnetically induced transparency(EIT)or electromagnetically induced absorption(EIA)are fundamental physics principles behind the stage.Furthermore,various techniques such as amplitude-or frequency-modulation,optical homodyne read-out,microwave superheterodyne and frequency conversion based on multi-wave mixing in atoms are utilized to push the metrics into higher levels.In this review,different technologies and the corresponding metrics they had achieved were presented,hoping to inspire more possibilities in the improvement of metrics of Rydberg atom-based electric field sensing and broadness of application scenarios.

Long-range adiabatic quantum state transfer through a linear array of quantum dots

We introduce an adiabatic long-range quantum communication proposal based on a quantum dot array.By adiabatically varying the external gate voltage applied on the system,the quantum information encoded in the electron can be transported from one end dot to another.We numerically solve the schr dinger equation for a system with a given number of quantum dots.It is shown that this scheme is a simple and efficient protocol to coherently manipulate the population transfer under suitable gate pulses.The dependence of the energy gap and the transfer time on system parameters is analyzed and shown numerically.We also investigate the adiabatic passage in a more realistic system in the presence of inevitable fabrication imperfections.This method provides guidance for future realizations of adiabatic quantum state transfer in experiments.

Quantum computation with surface-state electrons by rapid population passages

Quantum computation requires coherently controlling the evolutions of qubits.Usually,these manipulations are implemented by precisely designing the durations(such as theπ-pulses)of the Rabi oscillations and tunable interbit coupling.Relaxing this requirement,herein we show that the desired population transfers between the logic states can be deterministically realized(and thus quantum computation could be implemented)both adiabatically and non-adiabatically,by performing the duration-insensitive quantum manipulations.Our proposal is specifically demonstrated with the surface-state of electrons floating on the liquid helium,but could also be applied to the other artificially controllable systems for quantum computing.

Coarse and fine-tuning of lasing transverse electromagnetic modes in coupled all-inorganic perovskite quantum dots

Inorganic perovskite lasers are of particular interest,with much recent work focusing on Fabry-P6rot cavity-forming nanowires.We demonstrate the direct observation of lasing from transverse electromagnetic(TEM)modes with a long coherence time-9.5ps in coupled CsPbBr_(3) quantum dots,which dispense with an external cavity resonator and show how the wavelength of the modes can be controlled via two independent tuning-mechanisms.Controlling the pump power allowed us tofine-tune the TEM mode structure to the emission wavelength,thus providing a degree of control over the properties of the lasing signal.The temperature-tuning provided an additional degree of control over the wavelength of the lasing peak,importantly,maintained a constant full width at half maximum(FWHM)over the entire tuning range without mode-hopping.