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arXiv:1811.10704 · Science Advances

On-demand photonic entanglement synthesizer

Shuntaro Takeda, Kan Takase, Akira Furusawa

Published May 3, 2019• 75 citations
arXivHTMLPDF

Abstract

Quantum information protocols require various types of entanglement, such as Einstein-Podolsky-Rosen, Greenberger-Horne-Zeilinger, and cluster states. In optics, on-demand preparation of these states has been realized by squeezed light sources, but such experiments require different optical circuits for different entangled states, thus lacking versatility. Here, we demonstrate an on-demand entanglement synthesizer that programmably generates all these entangled states from a single squeezed light source. This is achieved by a loop-based circuit that is dynamically controllable at nanosecond time scales and processes optical pulses in the time domain. We verify the generation of five different small-scale entangled states and a large-scale cluster state containing more than 1000 modes without changing the optical circuit. Moreover, this circuit enables storage and release of one part of the generated entangled state, thus working as a quantum memory. Our demonstration should open a way for a more general entanglement synthesizer and a scalable quantum processor.

DOI
10.1126/sciadv.aaw4530

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Quantum information protocols require various types of entanglement, such as Einstein-Podolsky-Rosen, Greenberger-Horne-Zeilinger, and cluster states. In optics, on-demand preparation of these states has been realized by squeezed light sources, but such experiments require different optical circuits for different entangled states, thus lacking versatility. Here, we demonstrate an on-demand entanglement synthesizer that programmably generates all these entangled states from a single squeezed light source. This is achieved by a loop-based circuit that is dynamically controllable at nanosecond time scales and processes optical pulses in the time domain. We verify the generation of five different small-scale entangled states and a large-scale cluster state containing more than 1000 modes without changing the optical circuit. Moreover, this circuit enables storage and release of one part of the generated entangled state, thus working as a quantum memory. Our demonstration should open a way for a more general entanglement synthesizer and a scalable quantum processor.
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Abstract The central technological appeal of quantum science resides in exploiting quantum effects, such as entanglement, for a variety of applications, including computing, communication and sensing 1 . The overarching challenge in these fields is to address, control and protect systems of many qubits against decoherence 2 . Against this backdrop, optical photons, naturally robust and easy to manipulate, represent ideal qubit carriers. However, the most successful technique so far for creating photonic entanglement 3 is inherently probabilistic and, therefore, subject to severe scalability limitations. Here we report the implementation of a deterministic protocol 4–6 for the creation of photonic entanglement with a single memory atom in a cavity 7 . We interleave controlled single-photon emissions with tailored atomic qubit rotations to efficiently grow Greenberger–Horne–Zeilinger (GHZ) states 8 of up to 14 photons and linear cluster states 9 of up to 12 photons with a fidelity lower bounded by 76(6)% and 56(4)%, respectively. Thanks to a source-to-detection efficiency of 43.18(7)% per photon, we measure these large states about once every minute, which is orders of magnitude faster than in any previous experiment 3,10–13 . In the future, this rate could be increased even further, the scheme could be extended to two atoms in a cavity 14,15 or several sources could be quantum mechanically coupled 16 , to generate higher-dimensional cluster states 17 . Overcoming the limitations encountered by probabilistic schemes for photonic entanglement generation, our results may offer a way towards scalable measurement-based quantum computation 18,19 and communication 20,21 .
Abstract Quantum technology, leveraging non-classical characteristics, enables breakthroughs in computation, communication, and metrology. Entanglement generation is fundamental. However, efficiently creating large-scale entanglement remains challenging. Using 2 n physical modes within a single particle has been exploited for encoding n -qubit entanglement, yet this approach is believed to be unscalable. Here, using sequentially quantum correlations on a single particle, we present a Ququart Encoding scheme to encode and process multi-qubit entanglement within ququart. We implement a programmable integrated-photonic entanglement generator on a silicon chip, encoding up to 5-qubit entanglement and quantum circuits within 2 ququarts. Within a ququart, we generate high-fidelity 3-qubit W and Greenberger-Horne-Zeilinger states and verify quantum teleportation and phase estimation. Encoding a pair of entangled photons as ququarts yields a 5-qubit Greenberger-Horne-Zeilinger state at 688 Hz, with fidelity 0.956 ± 0.053, confirming genuine 5-qubit entanglement. While the 2 n physical-mode overhead persists for general purposes, our scheme reduces it from exponential to linear under certain circumstances, potentially accelerating large-scale quantum systems.