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Physical Review A

Single-step fabrication of scalable multimode quantum resources using four-wave mixing with a spatially structured pump

Hailong Wang, Claude Fabre, Jietai Jing

Published May 31, 2017• 63 citations
Publisher

Abstract

Multimode quantum resources or states, in which quantum correlations are shared and distributed among multiple parties, are important not only for fundamental tests of quantum effects but also for their numerous possible applications in quantum technologies, such as quantum imaging and quantum metrology. Here we demonstrate the single-step fabrication of a multimode quantum resource from four-wave mixing (FWM) process in hot Rb vapor using a spatially structured pump, which consists of a coherent combination of two tilted pump beams. During this FWM process, one probe beam is amplified, three conjugate and two new probe beams are generated. The measured degrees of the intensity squeezing for the four-beam case and six-beam case are around $\ensuremath{-}4.1\ifmmode\pm\else\textpm\fi{}0.1$ dB and $\ensuremath{-}4.7\ifmmode\pm\else\textpm\fi{}0.1$ dB, respectively. The generated multiple quantum correlated beams are naturally separated with distinct directions, which is crucial for sending them out to quantum nodes at different locations in quantum communication. Our scheme is compact, simple, phase insensitive, and easily scalable to larger number of quantum-correlated modes.

DOI
10.1103/physreva.95.051802

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Multimode quantum resources or states, in which quantum correlations are shared and distributed among multiple parties, are important not only for fundamental tests of quantum effects but also for their numerous possible applications in quantum technologies, such as quantum imaging and quantum metrology. Here we demonstrate the single-step fabrication of a multimode quantum resource from four-wave mixing (FWM) process in hot Rb vapor using a spatially structured pump, which consists of a coherent combination of two tilted pump beams. During this FWM process, one probe beam is amplified, three conjugate and two new probe beams are generated. The measured degrees of the intensity squeezing for the four-beam case and six-beam case are around \ensuremath−4.1\ifmmode±\else\textpm\fi0.1\ensuremath{-}4.1\ifmmode\pm\else\textpm\fi{}0.1\ensuremath−4.1\ifmmode±\else\textpm\fi0.1 dB and \ensuremath−4.7\ifmmode±\else\textpm\fi0.1\ensuremath{-}4.7\ifmmode\pm\else\textpm\fi{}0.1\ensuremath−4.7\ifmmode±\else\textpm\fi0.1 dB, respectively. The generated multiple quantum correlated beams are naturally separated with distinct directions, which is crucial for sending them out to quantum nodes at different locations in quantum communication. Our scheme is compact, simple, phase insensitive, and easily scalable to larger number of quantum-correlated modes.
Quantum correlations and entanglement shared among multiple quantum modes are important for both fundamental science and the future development of quantum technologies. This development will also require an efficient quantum interface between multimode quantum light sources and atomic ensembles, which makes it necessary to implement multimode quantum light sources that match the atomic transitions. Here, we report on such a source that provides a method for generating quantum correlated beams that can be extended to a large number of modes by using multiple four-wave mixing (FWM) processes in hot rubidium vapor. Experimentally, we show that two cascaded FWM processes produce strong quantum correlations between three bright beams but not between any two of them. In addition, the intensity-difference squeezing is enhanced with the cascaded system to -7.0±0.1 dB from the -5.5±0.1/-4.5±0.1 dB squeezing obtained with only one FWM process. One of the main advantages of our system is that as the number of quantum modes increases, so does the total degree of quantum correlations. The proposed method is also immune to phase instabilities due to its phase insensitive nature, can easily be extended to multiple modes, and has potential applications in the production of multiple quantum correlated images.
Extensive attention has been drawn in generating multimode quantum states in recent years. Many efforts have been made during the last decade to produce such states. In this paper, we have experimentally demonstrated a scheme for generating a multi-spatial-mode quantum light source by a non-degenerated four-wave mixing process with a conical pump and a conical probe in a hot atomic vapor cell. The degree of the intensity-difference squeezing between the generated twin beams is about −4.1 dB. Due to the similar conical shape of the concentric quantum correlated beams, both the amplified probe and the generated conjugate beams can be decomposed into many angular modes. We have also experimentally verified the multi-spatial-mode nature of the generated quantum correlation by comparing the noise levels' variation tendencies of global attenuation and local cutting attenuations. In addition, we have also found the optimal values of each parameter in this scheme for further applications. Due to our scheme's advantages such as compactness, phase-insensitivity, and easy scalability, we have already shown a promising candidate for generating multi-spatial-mode quantum states, which may find potential applications in quantum metrology and quantum imaging, such as quantum-enhanced superresolution and the generation of multiple quantum correlated images.
Multimode quantum states, such as multipartite quantum entanglement or quantum correlations, are important for both fundamental science and the future development of quantum technologies. Here we theoretically propose and experimentally realize a scheme that can fully exploit the multi-spatial-mode nature of the four-wave-mixing (FWM) process, i.e., spatial multiplexing, and thus integrates multiple FWM processes into a single cell at each stage of the cascaded process. The number of generated quantum-correlated beams 2n{2}^{n}2n is exponentially dependent on the number of vapor cells nnn. In addition, the quantum correlations between the multiple beams also increase as the number of vapor cell increases. For the case of n=2n=2n=2, we experimentally show that the degree of intensity-difference squeezing between the four quantum-correlated beams in our scheme is enhanced to $\ensuremath{-}8.2\ifmmode\pm\else\textpm\fi{}0.2$ dB from $\ensuremath{-}5.6\ifmmode\pm\else\textpm\fi{}0.3$ and $\ensuremath{-}6.5\ifmmode\pm\else\textpm\fi{}0.2$ dB of squeezing obtained with a single FWM process. Our system may find applications in quantum information and precision measurement.
Generation of multimode quantum states has drawn much attention recently due to its importance for both fundamental science and the future development of quantum technologies. Here, by using a four-wave mixing process with a conical pump beam, we have experimentally observed about -3.8 dB of intensity-difference squeezing between a single-axial probe beam and a conical conjugate beam. The multi-spatial-mode nature of the generated quantum-correlated beams has been shown by comparing the variation tendencies of the intensity-difference noise of the probe and conjugate beams under global attenuation and local cutting attenuation. Due to its compactness, phase-insensitive nature, and easy scalability, our scheme may find potential applications in quantum imaging, quantum information processing, and quantum metrology.
We have experimentally shown in a recent paper [Wang et al., Phys. Rev. A 95, 051802(R) (2017)] that a four-wave mixing (FWM) process in a Rb vapor with a spatially structured pump (SSP), consisting of a coherent combination of two tilted pump beams, can generate six well-separated bright beams that are quantum correlated. The experimental setup is compact, simple, phase insensitive, and easily scalable to a larger number of quantum correlated beams. For applications to quantum information processing, multipartite entanglement is needed in addition to quantum correlations. Very recently, we have also experimentally demonstrated the generation of the hexapartite entanglement from this SSP-based FWM process [Zhang et al., Phys. Rev. Lett. 124, 090501 (2020)]. The purpose of this theoretical paper is to extensively investigate the hexapartite entanglement properties by using different entanglement witnesses such as the van Loock-Furusawa criterion and the positivity under partial transposition criterion. We find that hexapartite entanglement is indeed present among the six beams. In addition, we also study the supermodes of this system using basis change.
Abstract We report the quantum correlated triple beams via cascaded four-wave mixing (CFWM) amplified in single hot atomic vapor. Experimentally, we show that strong quantum correlation of three light beams, among them any two’s quantum correlation is characterized by the maximum value of intensity-difference squeezing (IDS) about −7.8 ± 0.3 dB. We found there is IDS between two idler beams, because two pairs of Einstein–Podolsky–Rosen injections potentially exist in our system. Besides, CFWM can emit three-mode beams at three different frequencies, in which these beams can be well separated in the spatial domain. Moreover, much difference with other methods, the injecting probe field can manipulate the gain and IDS of output three-mode light beams, which is resulting from competition relationship between cascaded two four-wave mixing processes. More interestingly, Autler–Townes splitting of gain peaks of output signals due to dressing effect of pumping fields, will lead to the evolution of measured two- and three-mode IDS from single-mode to multi-mode at frequency domain. This result will provide a multimode quantum resource which can potentially realize multimode entanglement and quantum networks.