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arXiv:2101.10089 · Physical Review A

Hyper-hybrid entanglement, indistinguishability, and two-particle entanglement swapping

Soumya Das, Goutam Paul, Anindya Banerji

Published Nov 2, 2020• 11 citations
arXivHTMLPDF

Abstract

Hyper-hybrid entanglement for two indistinguishable bosons has been recently proposed by Li et al. [Y. Li, M. Gessner, W. Li, and A. Smerzi, Phys. Rev. Lett. 120, 050404 (2018)]. In the current paper, we show that this entanglement exists for two indistinguishable fermions also. Next, we establish two no-go results: no hyper-hybrid entanglement for two distinguishable particles, and no unit fidelity quantum teleportation using indistinguishable particles. If either of these is possible, then the no-signaling principle would be violated. While several earlier works have attempted extending many results on distinguishable particles to indistinguishable ones, and vice versa, the above two no-go results establish a nontrivial separation between the two domains. Finally, we propose an efficient entanglement swapping using only two indistinguishable particles, whereas a minimum number of either three distinguishable or four indistinguishable particles is necessary for existing protocols.

DOI
10.1103/physreva.102.052401

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Hyper-hybrid entanglement for two indistinguishable bosons has been recently proposed by Li et al. [Y. Li, M. Gessner, W. Li, and A. Smerzi, Phys. Rev. Lett. 120, 050404 (2018)]. In the current paper, we show that this entanglement exists for two indistinguishable fermions also. Next, we establish two no-go results: no hyper-hybrid entanglement for two distinguishable particles, and no unit fidelity quantum teleportation using indistinguishable particles. If either of these is possible, then the no-signaling principle would be violated. While several earlier works have attempted extending many results on distinguishable particles to indistinguishable ones, and vice versa, the above two no-go results establish a nontrivial separation between the two domains. Finally, we propose an efficient entanglement swapping using only two indistinguishable particles, whereas a minimum number of either three distinguishable or four indistinguishable particles is necessary for existing protocols.
This thesis investigates the entanglement of distinguishable and indistinguishable particles, introducing a new error model for Hardy's test, experimentally verified using superconducting qubits. We address challenges in implementing quantum protocols based on this test and propose potential solutions and present two performance measures for qubits in superconducting quantum computers. We demonstrate that if quantum particles can create hyper-hybrid entangled states and achieve unit fidelity quantum teleportation, arbitrary state cloning is possible. This leads to two no-go theorems: hyper-hybrid entangled states cannot be formed with distinguishable particles, and unit fidelity quantum teleportation is unattainable with indistinguishable particles. These results establish unique correlations for each particle type, creating a clear distinction between the two domains. We also show that hyper-hybrid entangled states can be formed with indistinguishable fermions and generalize this for both fermions and bosons. We develop a generalized DoF trace-out rule applicable to single or multiple degrees of freedom for both types of particles. This framework allows us to derive expressions for teleportation fidelity and singlet fraction, establishing an upper bound for the generalized singlet fraction. We present an optical circuit that generates entanglement in distinguishable particles. Using our trace-out rule, we show that for two indistinguishable particles with multiple DoFs, the monogamy of entanglement can be maximally violated. We assert that indistinguishability is essential for this violation in qubit systems. For three indistinguishable particles, we confirm that monogamy is upheld using squared concurrence. Finally, we propose a novel entanglement swapping protocol involving two indistinguishable particles, enhancing quantum networks and quantum repeaters.
Entanglement swapping represents an important protocol for transferring information within quantum networks. Here we present a scheme to implement entanglement swapping with independently-prepared identical particles (bosons or fermions), exploiting the indistinguishability due to their spatial overlap. In this protocol no initial entangled pairs are required and, for fermions, even Bell state measurements have not to be performed. These features constitute both a conceptual and practical advance compared to the standard procedure. The scheme is straightforwardly extended to multiple swapping, which is basic for quantum repeaters and relays in quantum information processing.
The wave-particle duality of light has led to two different encodings of optical quantum information. One approach, referred to as the discrete-variable (DV) one, relies on finite dimensional quantum systems, while the other one, referred to as the continuous-variable (CV) one, is based on wave-like states belonging to an infinite dimensional Hilbert space. These two encodings have historically been separated, but recently, new hybrid protocols which aim at combining the advantages of the two encodings have emerged [1] . In that prospect our recent demonstration of the measurement-induced generation of hybrid entanglement between discrete- and continuous-variable quantum states [2] , [3] , located at distant places and connected by a lossy channel, has opened the way to the implementation of hybrid protocols and heterogeneous quantum networks. Following the first protocols based on this resource, such as the remote preparation of continuous-variable qubits [4] , or a violation of an Einstein-Podolsky-Rosen steering inequality [5] , we will here report our latest experimental results on entanglement swapping and quantum teleportation protocols using hybrid entangled states based on different encodings [6] .
Summary form only given. Entanglement is the resource that makes quantum communication and quantum computation work. The most basic quantum communication protocols are quantum cryptography, quantum teleportation and entanglement swapping. In quantum teleportation one of two parties wants to send the other one a quantum state using some independent carrier. Entanglement swapping in its simplest form is the use of quantum teleportation to transmit a quantum state that is already entangled with some other state. Thereby the entanglement that existed between the original particle and its partner is transferred to the output particle. Both teleportation and entanglement swapping have successfully been demonstrated. However, in none of the experiments the quality of teleportation was high enough to produce output correlations that could have violated a Bell-type inequality. In this work we will show that qubit teleportation using polarization-entangled photon pairs can produce the desired correlations.
While the concept of entanglement for distinguishable particles is well established, defining entanglement and nonlocality in systems of indistinguishable particles, which require the use of the (anti)symmetrization postulate, remains challenging, and multiple approaches have been proposed to address this issue. In this work we study the problem of detecting genuine tripartite entanglement among systems of indistinguishable bosons. A genuine entangled state is one that cannot be separable under any bipartition, where separability in the indistinguishable regime is defined by the existence of single-particle properties within each subsystem, without the possibility of knowing which property belongs to which subsystem. We use an algorithm that allows us to search for these single-particle properties and consequently rank states according to their degree of separability. In particular, we introduce a state of indistinguishable bosons with properties analogous to those of the standard Greenberger-Horne-Zeilinger state.
Recently, it has been realized that indistinguishability is a resource for quantum information processing. A new method to represent the indistinguishable particles by Franco et al. (Sci Rep 6:20603, 2016, https://doi.org/10.1038/srep20603 ) and measure the concurrence is developed by Nosrati et al. (npj Quantum Inf 6:39, 2020, https://doi.org/10.1038/s41534-020-0271-7 ). The monogamy property says that quantum entanglement cannot be shared freely between more than two particles. For three distinguishable particles, the monogamy of entanglement was first expressed as an inequality using squared concurrence where each particle has a single degree of freedom (for pure or mixed states). Using multiple degrees of freedom, similar inequality was shown to be held between two distinguishable particles. However, for two indistinguishable particles, where each particle cannot be addressed individually, the monogamy inequality was shown to be violated maximally for a specific state. Thus a question naturally arises: what happens to the monogamy of entanglement in the case of three or more indistinguishable particles? We prove that monogamy holds in this scenario and the inequality becomes equality for all pure indistinguishable states. Further, we provide three major operational meanings of our result. Finally, we present an experimental schematic using photons to observe our result.