Driving non-Gaussian to Gaussian states with linear optics

Driving two atoms in an optical cavity into an entangled steady state using engineered decay

We propose various schemes for the dissipative preparation of a maximally entangled steady state of two atoms in an optical cavity. Harnessing the natural decay processes of cavity photon loss and spontaneous emission, we use an effective operator formalism to identify and engineer effective decay processes, which reach an entangled steady state of two atoms as the unique fixed point of the dissipative time evolution. We investigate various aspects that are crucial for the experimental implementation of our schemes in present-day and future cavity quantum electrodynamics systems and analytical…

Photon number and optical tomograms for Gaussian states

A review of probability representation of quantum states in given for optical and photon number tomography approaches. Explicit connection of photon number tomogram with measurable by homodyne detector optical tomogram is obtained. New integral relations connecting Hermite polynomials of two variables with Laguerre polynomials are found. Examples of generic Gaussian photon states (squeezed and correlated states) are studied in detail.

High-efficiency single-photon Fock state production by transitionless quantum driving

Single photon source is one of the key devices for optical quantum information processing. Differing from the usual stimulated Raman adiabatic passage to obtain single-photon radiation, here we propose an approach to produce optical Fock state on demand in the usual atom-cavity system by utilizing the technique of transitionless quantum driving. The present proposal effectively suppresses the unwanted but practically unavoidable nonadiabatic transitions in the previous adiabatic schemes. Therefore, the efficiency of Fock state production by the present technique could be significantly high, ev…

Indirect driving of cavity QED system and its induced non-linearity

The linear driving for a single-mode optical field in a cavity can result from the external driving of classical field even when the coupling between the classical field and the cavity is weak. We revisit this well known effect with a microscopic model where a classical field is applied to a wall of the cavity to excite the atoms in the wall, and re-combination of the low excitations of the wall mediates a linear driving for the single-mode field inside the cavity. With such modeling about the indirect driving through the quantum excitations of the wall, we theoretically predict several non-li…

Building Gaussian Cluster States by Linear Optics

The linear optical creation of Gaussian cluster states, a potential resource for universal quantum computation, is investigated. We show that for any Gaussian cluster state, the canonical generation scheme in terms of QND-type interactions, can be entirely replaced by off-line squeezers and beam splitters. Moreover, we find that, in terms of squeezing resources, the canonical states are rather wasteful and we propose a systematic way to create cheaper states. As an application, we consider Gaussian cluster computation in multiple-rail encoding. This encoding may reduce errors due to finite squ…

Capacity of optical communication in loss and noise with general Gaussian receivers

Laser-light (coherent-state) modulation is sufficient to achieve the ultimate (Holevo) capacity of classical communication over a lossy and noisy optical channel, but requires a receiver that jointly detects long modulated codewords with highly nonlinear quantum operations, which are near-impossible to realize using current technology. We analyze the capacity of the lossy-noisy optical channel when the transmitter uses coherent state modulation but the receiver is restricted to a general quantum-limited Gaussian receiver, i.e., one that may involve arbitrary combinations of Gaussian operations…

Gaussian benchmark for optical communication aiming towards ultimate capacity

We establish the fundamental limit of communication capacity within Gaussian schemes under phase-insensitive Gaussian channels, which employ multimode Gaussian states for encoding and collective Gaussian operations and measurements for decoding. We prove that this Gaussian capacity is additive, i.e., its upper bound occurs with separable encoding and separable receivers so that a single-mode communication suffices to achieve the largest capacity under Gaussian schemes. This rigorously characterizes the gap between the ultimate Holevo capacity and the capacity within Gaussian communication, sho…

手性波导量子电动力学介导的非线性光学：动量反关联光子对的产生

Nonlinear Optics Mediated by Chiral Waveguide QED: Generation of Momentum-anticorrelated Photon Pairs

研究手性波导量子电动力学介导的非线性光学，通过全波函数计算等方法，揭示跨导量子比特耦合后透射光非相干成分性质，表明其主要源于双光子过程，波导与局部驱动相互作用可调控透射场量子统计，使\(g^{(2)}(0)\)可调。

亮压缩光驱动高次谐波产生中的高斯纠缠与非高斯性涌现

Emergence of Gaussian entanglement and non-Gaussianity in high-harmonic generation driven by bright squeezed light

研究亮压缩真空驱动高次谐波产生中非经典高斯态的涌现条件，发现双色驱动下偶次谐波响应近似线性于压缩场正交分量，导致多模高斯纠缠，并表征其协方差矩阵、纠缠结构和量子隐形传态保真度。

Non-Uniqueness of Non-Linear Optical Response

In recent years, non-linear optical phenomena have attracted much attention, with a particular focus on the engineering and exploitation of non-linear responses. Comparatively little study has however been devoted to the driving fields that generate these responses. In this work, we demonstrate that the relationship between a driving field and the optical response it induces is non-unique. Using a generic model for a strongly interacting system, we show that multiple candidate driving field exists, which will all generate the same response. Consequently, it is possible show that the optical re…

在驱动量子振子的马尔可夫主方程下高斯混合态的演化

Evolution of Gaussian mixed states under the Markovian master equation for a driven quantum oscillator

研究了线性位移或驱动谐振子的通用量子马尔可夫主方程，揭示了在线性驱动力下快速旋转模式不影响系统位移动力学，推导了高斯混合态量子主方程的解析解，并讨论了外部时间依赖力对位移动力学的影响。

Many-Body Dissipative Flow of a Confined Scalar Bose-Einstein Condensate Driven by a Gaussian Impurity

The many-body dissipative flow induced by a mobile aussian impurity harmonically oscillating within a cigar-shaped Bose-Einstein condensate is investigated. For very {small and large driving frequencies} the superfluid phase is preserved. Dissipation is identified, for intermediate driving frequencies, by the non-zero value of the drag force whose abrupt increase {signals the spontaneous downstream emission of an array of gray solitons. After each emission event, typically each of the solitary waves formed decays and splits into two daughter gray solitary waves that are found to be robust prop…