Experimental enhancement of six-beam quantum squeezing by phase-sensitive cascaded four-wave mixing processes.

We experimentally realize the enhancement of six-beam quantum squeezing by utilizing a six-beam phase-sensitive amplifier (PSA) based on cascaded four-wave mixing processes. Compared to the intensity-difference squeezing (IDS) of about 5.03 or 5.

All-optical Einstein-Podolsky-Rosen steering swapping.

Einstein-Podolsky-Rosen (EPR) steering, an important resource in quantum information, describes the ability of one party to influence the state of another party through local measurements. It differs from Bell nonlocality and entanglement due to its asymmetric property. EPR steering swapping allows two spatially independent parties to present EPR steering without direct interaction.

Deterministic All-Optical Continuous-Variable Quantum Telecloning.

Quantum telecloning, a pivotal multiuser quantum communication protocol in the realm of quantum information science, facilitates the copy of a quantum state across M distinct locations through teleportation technique. In the continuous-variable regime, the implementation of quantum telecloning necessitates the distribution of multipartite entanglement among the sender and M receiver parties. Following this, the sender carries out optic-electro conversion and transmits information via classical channel to M spatially separated receivers simultaneously.

Deterministic All-Optical Quantum Teleportation of Four Degrees of Freedom.

Quantum teleportation, disembodied transfer of the unknown quantum state between two locations, has been experimentally demonstrated for both discrete and continuous variable states in one degree of freedom (DOF). Generally, multiple DOFs are needed to fully characterize a quantum state. Therefore, to implement intact quantum teleportation, multiple DOFs of quantum state should be teleported simultaneously.

Orbital Angular Momentum Multiplexed Deterministic All-Optical Quantum Erasure-Correcting Code.

Quantum erasure-correcting code, which corrects the erasure in the transmission of quantum information, is an important protocol in quantum information. In the continuous variable regime, the feed-forward technique is needed for realizing quantum erasure-correcting code. This feed-forward technique involves optic-electro and electro-optic conversions, limiting the bandwidth of quantum erasure-correcting code.

Enhancing and flattening multiplexed quantum entanglement by utilizing perfect vortex modes.

We experimentally demonstrate a method for enhancing and flattening multiplexed entanglement in the four-wave mixing (FWM) process, which is implemented by replacing Laguerre-Gaussian (LG) modes with perfect vortex (PV) modes. For the topological charge l ranging from -5 to 5, the entanglement degrees of orbital angular momentum (OAM) multiplexed entanglement with PV modes are all larger than those of OAM multiplexed entanglement with LG modes. More importantly, for OAM multiplexed entanglement with PV modes, the degree of entanglement almost does not change with the topology value.

Phase-insensitive amplifier gain estimation at Cramér-Rao bound for two-mode squeezed state of light.

Phase-insensitive amplifiers (PIAs), as a class of important quantum devices, have found significant applications in the subtle manipulation of multiple quantum correlation and multipartite quantum entanglement. Gain is a very important parameter for quantifying the performance of a PIA. Its absolute value can be defined as the ratio of the output light beam power to the input light beam power, while its estimation precision has not been extensively investigated yet.

Experimental measurement of quadrature squeezing in quadripartite entanglement.

Multipartite entanglement is one of the most fundamental and important resources for quantum information processing in both discrete variable and continuous variable (CV) regimes. For its applications in the CV regime, such as the realization of quantum teleportation networks and quantum dense coding, the quadrature squeezing of multipartite entanglement plays a significant role. Here, we report the first, to the best of our knowledge, experimental measurement of the quadrature squeezing in the quadripartite entanglement generated by the two-beam pumped cascaded four-wave mixing process in a vapor cell.

Ultra-Large-Scale Deterministic Entanglement Containing 2×20 400 Optical Modes Based on Time-Delayed Quantum Interferometer.

Quantum entanglement is an indispensable resource for implementing quantum information processing. The scale of quantum entanglement directly determines its quantum information processing capability. Therefore, it is of great importance to generate ultra-large-scale (ULS) quantum entanglement for the development of quantum information science and technology.

Self-healing of Einstein-Rosen-Podolsky steering after an obstruction.

Einstein-Rosen-Podolsky (EPR) steering describes the "spooky action at a distance" that one party can instantaneously affect the states of another distant party if they share quantum correlations. Due to its intriguing properties, EPR steering is recognized as an essential resource for a number of quantum information tasks. However, EPR steering may be destroyed when distributed in practical environments.

All-Optical Entanglement Swapping.

Entanglement swapping, which is a core component of quantum network and an important platform for testing the foundation of quantum mechanics, can enable the entangling of two independent particles without direct interaction both in discrete variable and continuous variable systems. Conventionally, the realization of entanglement swapping relies on the Bell-state measurement. In particular, for entanglement swapping in continuous variable regime, such Bell-state measurement involves the optic-electro and electro-optic conversion, which limits the applications of the entanglement swapping for constructing broadband quantum network.

Phase manipulated two-mode entangled state from a phase-sensitive amplifier.

The phase manipulation of the two-mode entangled state, which can flexibly control the combination of quadrature components on demand, is important for continuous variable (CV) quantum information and quantum metrology. Here, we experimentally demonstrate the phase manipulation of entangled state by using a phase-sensitive amplifier (PSA) based on four-wave mixing (FWM) process. The entanglement with different phase space squeezing orientations can be generated by directly changing the phase of the PSA.

Orbital Angular Momentum Multiplexed Quantum Dense Coding.

To beat the channel capacity limit of conventional quantum dense coding (QDC) with fixed quantum resources, we experimentally implement the orbital angular momentum (OAM) multiplexed QDC (MQDC) in a continuous variable system based on a four-wave mixing process. First, we experimentally demonstrate that the Einstein-Podolsky-Rosen entanglement source coded on OAM modes can be used in a single channel to realize the QDC scheme. Then, we implement the OAM MQDC scheme by using the Einstein-Podolsky-Rosen entanglement source coded on OAM superposition modes.

Multidimensional four-wave mixing signals detected by quantum squeezed light.

Four-wave mixing (FWM) of optical fields has been extensively used in quantum information processing, sensing, and memories. It also forms a basis for nonlinear spectroscopies such as transient grating, stimulated Raman, and photon echo where phase matching is used to select desired components of the third-order response of matter. Here we report an experimental study of the two-dimensional quantum noise intensity difference spectra of a pair of squeezed beams generated by FWM in hot Rb vapor.

Experimental Demonstration of a Multifunctional All-Optical Quantum State Transfer Machine.

Quantum information protocol with quantum resources shows a great advantage in substantially improving security, fidelity, and capacity of information processing. Various quantum information protocols with diverse functionalities have been proposed and implemented. However, in general, the present quantum information system can only carry out a single information protocol or deal with a single communication task, which limits its practical application in the future.

Nonlinear interferometric surface-plasmon-resonance sensor.

A nonlinear interferometer can be constructed by replacing the beam splitter in the Mach-Zehnder interferometer with four-wave mixing (FWM) process. Meanwhile, the conventional surface plasmon resonance (SPR) sensors can be extensively used to infer the information of refractive index of the sample to be measured via either angle demodulation technique or intensity demodulation technique. Combined with a single FWM process, a quantum SPR sensor has been realized, whose noise floor is reduced below standard quantum limit with sensitivity unobtainable with classical SPR sensor.

All-Optical Optimal N-to-M Quantum Cloning of Coherent States.

The laws of quantum mechanics forbid the perfect copying of an unknown quantum state, known as the no-cloning theorem. In spite of this, approximate cloning with imperfect fidelity is possible, which opens up the field of quantum cloning. In general, quantum cloning can be divided into discrete variable and continuous variable (CV) categories.

Characterization of quantum squeezing generated from the phase-sensitive and phase-insensitive amplifiers in the ultra-low average input photon number regime.

We give the general expressions of intensity-difference squeezing (IDS) generated from two types of optical parametric amplifiers [i.e. phase-sensitive amplifier (PSA) and phase-insensitive amplifier (PIA)] based on the four-wave mixing process, which clearly shows the IDS transition between the ultra-low average input photon number regime and the ultra-high average input photon number regime.

Large-Scale Quantum Network over 66 Orbital Angular Momentum Optical Modes.

Multipartite entanglement (ME) is the fundamental ingredient for building quantum networks. The scale of ME determines its quantum information carrying and processing capability. Most of the current efforts for boosting the scale of ME focus on increasing the number of entangled nodes.

Orbital angular momentum multiplexed deterministic all-optical quantum teleportation.

Quantum teleportation is one of the most essential protocol in quantum information. In addition to increasing the scale of teleportation distance, improving its information transmission capacity is also vital importance for its practical applications. Recently, the orbital angular momentum (OAM) of light has attracted wide attention as an important degree of freedom for realizing multiplexing to increase information transmission capacity.

Enhancement of quantum correlations using correlation injection scheme in a cascaded four-wave mixing processes.

Quantum correlations and entanglement shared among multiple quantum beams are important for both fundamental science and the development of quantum technologies. The enhancement for them is necessary and important to implement the specific quantum tasks and goals. Here, we report a correlation injection scheme (CIS) which is an effective method to enhance the quantum correlations and entanglement in the symmetrical cascaded four-wave mixing processes, and the properties of quantum correlations and entanglement can be characterized by the values of the degree of intensity-difference squeezing (DS) and the smallest symplectic eigenvalues, respectively.

Reconfigurable Hexapartite Entanglement by Spatially Multiplexed Four-Wave Mixing Processes.

Multipartite entanglement serves as a vital resource for quantum information processing. Generally, its generation requires complex beam splitting processes which limit scalability. A promising trend is to integrate multiple nonlinear processes into a single device via frequency or time multiplexing.

Deterministic Generation of Orbital-Angular-Momentum Multiplexed Tripartite Entanglement.

We demonstrate the experimental generation of orbital angular momentum (OAM) multiplexed multipartite entanglement with cascaded four-wave mixing processes in a continuous variable (CV) system. In particular, we implement the simultaneous generation of 9 sets of OAM multiplexed tripartite entanglement over 27 Laguerre-Gauss (LG) modes, as well as 20 sets of OAM multiplexed bipartite entanglement over 40 LG modes, which show the rich entanglement structure of the system. In addition, we also generate tripartite entanglement of three types of coherent OAM superposition modes.

Experimental characterization of multiple quantum correlated beams in two-beam pumped cascaded four-wave mixing process.

We experimentally explore the relationships between the number of multiple quantum correlated beams generated by two-beam pumped cascaded four-wave mixing (CFWM) process and the system parameters, such as the angle between the two pump beams, one-photon detuning and two-photon detuning. We find that all of three system parameters can influence the number of multiple quantum correlated beams. Under the optimal system parameters, we can observe the emission of up to 14 quantum correlated beams with the intensity-difference squeezing of -6.

Interference-Induced Quantum Squeezing Enhancement in a Two-beam Phase-Sensitive Amplifier.

We experimentally demonstrate a method for realizing quantum squeezing enhancement which is induced by the interference in a two-beam phase-sensitive amplifier (PSA) based on a four-wave mixing process. Compared to the normal phase-insensitive amplifier with an intensity-difference squeezing (IDS) of 8.97±0.