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Hybrid Quantum Light – Hy-Light

Hybrid Quantum Light

In this project we investigate quantum states of light entangling single photon qubits with bright qubits encoded in coherent states with opposite phases. We study the fundamental properties of this kind of states as well as their applications to quantum computing and quantum communication.

Hybrid light as a novel high-impact resource for quantum technologies

The Hy-Light project participates in the current efforts for the design and realization of suitable quantum resources for the processing and transfer of information encoded in photonic quantum states. <br />The wave-particle duality of light has led to two traditionally-separated encodings of information: a ‘discrete-variable’ (DV) approach, based for instance on single photons, and a ‘continuous-variable’ (CV) one, which relies on continuous degrees of freedom such as amplitude and phase of a light field. Both regimes present specific advantages and drawbacks. In this context, very recently, hybridization between DV and CV tools and concepts has been identified as an important new resource allowing benefiting of the advantages of both optical continuous variables and discrete variables at the same time. Hy-Light joins the international researches on hybrid-entanglement resources. Its objective is to investigate and harness optical hybrid-entanglement, in the perspective of experimentally (and theoretically) validating its potentiality as a novel high-impact resource for quantum technologies.

The projet objective is to investigate and harness optical hybrid-entanglement, in the perspective of experimentally (and theoretically) validating its potentiality as a novel high-impact resource for quantum technologies.
To achieve such a goal, the project gathers two experimental groups at Institut de Physique de Nice (inPhyni) and Laboratoire Kastler Brossel (LKB), showing complementary skills, and of a theoretical partner at Laboratoire Matériaux et Phénomènes Quantiques (MPQ), who has repeatedly worked with experimental teams. The project has a strong exploratory component. To comply with the difficulties than arise by extreme youth of the topic, the groups will methodically explore enhanced and novel forms of DV-CV entanglement together with relevant non-classicality and entanglement witnesses. On these bases they will then move to the conception and experimental implementation of first advanced quantum computing and quantum communication protocols. The overall effort will not only deepen the general understanding of hybrid systems, but also casts the basis for future technologies exploring the best of DV and CV worlds.

The INPHYNI partner has identified a theoretical protocol leading to the generation of the desired hybrid state with time-bin encoding, by considering realistic experimental resources and limitations. The partner also focused on the miniaturization of the experiment fundamental bricks on a single photonic circuit. The LKB team focused on the remote preparation of arbitrary continuous-variable qubits based on loss-tolerant hybrid entanglement. A second work concerned the violation of a EPR steering inequality using hybrid entanglement. The MPQ focused on designing a loss-resistant entanglement witness of the canonical hybrid state based on single-rail encoding on the DV part.

This project is extremely exploratory. We expect from it original characterization tools, robust implementations and new architectures. Beyond its impact on the foundations of quantum physics, entanglement is a key tool in most quantum information and computation protocols. In this sense, the study of a new resource in this field of research will have a significant impact on both fundamental aspects in quantum optics and applications in quantum information. Due to its dual nature, hybrid entanglement will require advanced tools in order be characterized and lead to original results: these will include original protocols for the conceptions of a new kinds of hybrid entangled states, together with related witnesses and the investigation of quantum information protocols exploiting hybrid entanglement as enabling resource. Successes in the proposed tasks will constitute decisive advances in our understanding of hybrid approach: in this sense, the project will have a large impact on both fundamental quantum optics research and on its quantum information applications. This goal opens to the possibility of mid- and long-term applications, whose high societal and economic impact matches strategic objectives of information science and technology.

• Chip-based squeezing at a telecom wavelength, Photonics Research Vol. 7, Issue 7, pp. A36-A39 (2019)
• Quantum description of timing jitter for single-photon ON-OFF detectors, Phys. Rev. A 98, 013833 (2018)
• Hybrid entanglement with time-b

In quantum information sciences and technologies, light is an excellent candidate as information carrier due to the possibility of realizing optical qubits that can be transmitted though optical fibers, manipulated by means of linear optics and interfaced with matter.

The wave-particle duality of light has led to two traditionally-separated encodings of information: a ‘discrete-variable’ (DV) approach, based for instance on single photons, and a ‘continuous-variable’ (CV) one, which relies on continuous degrees of freedom such as amplitude and phase of a light field. Both regimes present specific advantages and drawbacks. DV approach has led to many groundbreaking experiments and allows achieving teleportation with close-to-unity fidelity but it is in most of the cases probabilistic and affected by single photon detector limitations. Conversely, CV approach can benefit from unconditional operations and unambiguous state discrimination but they suffer from strong sensitivity to losses and intrinsically limited fidelities.

In this context, very recently, hybridization between DV and CV tools and concepts has been foreseen as a key approach to gather the benefits from both regimes and to circumvent their individual limitations. Hy-Light enters into this emerging but potentially powerful endeavor. More specifically, the present research program will exploit as a fundamental resource hybrid entanglement between particle-like and wave-like optical qubits. This complex photonic resource that has been generated for the first time very recently brings together both DV and CV approaches and holds, among other, the promise of transferring information from an encoding to the other. Depending on the specific situation, it is thus possible to take alternatively advantage of CV or DV capabilities.

These promising features has motivated an increasing number of theoretical proposals involving hybrid entanglement as a resource for fundamental quantum optics as well as for QI. Nevertheless, the field is at its very early infancy and, so far, only two experimental realizations of hybrid entangled states have been demonstrated. Hy-Light takes the challenge to push these very first generation experiments towards new testable concepts and innovative protocol implementations to harness this potential approach. From a fundamental point of view, it will explore the non-classicality of hybrid states and develop novel adapted witnesses and characterization tools. It will also tackle the implementation of first advanced protocols in both quantum communication and quantum computing, using the potential of this yet unexplored photonic resource. The overall effort will not only deepen our understanding of such an hybrid approach, but also potentially casts the basis for future QI applications.

Project coordinator

Madame Virginia D Auria (Institut de Physique de Nice)

The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.

Partner

LKB Laboratoire Kastler Brossel
MPQ Laboratoire Matériaux et Phénomènes Quantiques
InPhyNi Institut de Physique de Nice

Help of the ANR 561,168 euros
Beginning and duration of the scientific project: January 2018 - 42 Months

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