Deterministic generation of large-scale hyperentanglement in three degrees of freedom

Entanglement serves as a fundamental resource for quantum information protocols,and hyperentanglement has received an increasing amount of attention for its high-capacity characteristic.Increasing the scale of hyperentanglement,i.e.,the number of modes in a hyperentangled system,is crucial for enhancing its capability in quantum information processing.Here,we demonstrate the generation of large-scale continuous-variable(CV)hyperentanglement in three degrees of freedom(DOFs),including azimuthal and radial indices of Laguerre–Gaussian(LG)modes and frequency.In our experiment,216 pairs of hyperentangled modes are deterministically generated from the four-wave mixing process in an atomic vapor.In addition,we show that the entanglement between coherent LG superposition modes denoted by both azimuthal and radial quantum numbers can also be generated from this system.Such large-scale CV hyperentanglement in three DOFs presents an efficient scheme to significantly increase the information capacity of the CV system.Our results provide a new platform for studying CV quantum information and open the avenue for constructing high-capacity parallel and multiple-DOF CV quantum information protocols.

Low-Noise Intensity Amplification of a Bright Entangled Beam

We experimentally demonstrate a low-noise phase-sensitive amplifier(PSA)scheme that is able to amplify bright entangled beams at a high level intensity gain of up to 4.4.Moreover,we demonstrate that the PSA scheme introduces much less uncorrelated extra noise to the entangled state than the phase-insensitive amplifier scheme with the same intensity gain.This PSA scheme has potential applications for quantum communication in continuous variable regimes.

Quantum-enhanced stochastic phase estimation with the Su(1,1)interferometer

Quantum stochastic phase estimation has many applications in the precise measurement of various physical parameters.Similar to the estimation of a constant phase,there is a standard quantum limit for stochastic phase estimation,which can be obtained with the Mach-Zehnder interferometer and coherent input state.Recently,it has been shown that the stochastic standard quantum limit can be surpassed with nonclassical resources such as squcezed light.However,practical methods to achieve quantum enhancement in the stochastic phase estimation remain largely unexplored.Here we propose a method utilizing the SU(1,1)interferometer and coherent input states to cstimate a stochastic optical phase.As an example,we investigate the Ornstcin-Uhlenback stochastic phase.We analyze the performance of this method for three key estimation problems:prediction,tracking,and smoothing.The results show significant reduction of the mean square error compared with the Mach-Zehnder interferometer under the same photon number flux inside the interferometers.In particular,we show that the method with the SU(1,1)interferometer can achieve fundamental quantum scaling,achieve stochastic Heisenberg scalinga and surpass the precision of the canonical measurement.

Deterministic all-optical quantum state sharing

Quantum state sharing,an important protocol in quantum information,can enable secure state distribution and reconstruction when part of the information is lost.In(k,n)threshold quantum state sharing,the secret state is encoded into n shares and then distributed to n players.The secret state can be reconstructed by any k players(k>n∕2),while the rest of the players get nothing.In the continuous variable regime,the implementation of quantum state sharing needs the feedforward technique,which involves opticelectro and electro-optic conversions.These conversions limit the bandwidth of the quantum state sharing.Here,to avoid the optic-electro and electro-optic conversions,we experimentally demonstrate(2,3)threshold deterministic all-optical quantum state sharing.A low-noise phase-insensitive amplifier based on the four-wave mixing process is utilized to replace the feedforward technique.We experimentally demonstrate that any two of three players can cooperate to implement the reconstruction of the secret state,while the rest of the players cannot get any information.Our results provide an all-optical platform to implement arbitrary(k,n)threshold deterministic all-optical quantum state sharing and pave the way to construct the all-optical broadband quantum network.

Quantum squeezing enhancement based on phase-sensitive cascaded four-wave mixing processes

Quantum squeezing is an important quantum resource for quantum metrology as it can improve the measurement precision.By enhancing the quantum squeezing level,the measurement precision can be further improved.Here,we experimentally implement quantum squeezing enhancement based on phase-sensitive cascaded four-wave mixing(CFWM)processes.The intensitydifference squeezing(IDS)between the two outputs of the phase-sensitive CFWM processes is enhanced to about 7.42 dB compared with IDS generated by the single four-wave mixing(FWM)process(about 3.31 or 4.01 dB).Such enhancement is enabled by both the intrinsic interference nature of phase-sensitive CFWM processes and the contribution of more gain from the two FWM processes.In addition,we measure IDS levels generated by phase-sensitive CFWM processes at different internalphase-locking points,which shows that the internal phase plays an important role in IDS enhancement.Our scheme provides a new method for improving the degree of IDS and may find potential applications in enhancing the measurement precision in quantum metrology.

Optical quantum states based on hot atomic ensembles and their applications

The four-wave mixing process in atomic ensembles has many important applications in quantum information.We review recent progress on the generation of optical quantum states from the four-wave mixing process in hot atomic ensembles,including the production of two-beam,multi-beam,and multiplexed quantum correlated or entangled states.We also review the applications of these optical quantum states in implementing quantum information protocols,constructing SU(1,1)quantum interferometers,and realizing quantum plasmonic sensing.These applications indicate that the four-wave mixing process in hot atomic ensembles is a promising platform for quantum information processing,especially for implementing alloptical quantum information protocols,constructing SU(1,1)interferometers,and realizing quantum sensing.