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Bulletin of the American Physical Society

Generation of heralded entanglement between distant quantum dot hole spins

Aymeric Delteil

Published Mar 17, 2016• 0 citations
OpenAlex

Abstract

Entanglement plays a central role in fundamental tests of quantum mechanics as well as in the burgeoning field of quantum information processing. Particularly in the context of quantum networks and communication, a major challenge is the efficient generation of entanglement between distant stationary (spin) qubits. Here, we report the realization of heralded quantum entanglement between two semiconductor quantum dot spins separated by more than five meters. Our results extend the previous demonstrations of distant spin entanglement in single trapped ions or neutral atoms, in atom ensembles and nitrogen vacancy centers to the domain of artificial atoms in semiconductor nanostructures that allow for onchip integration of electronic and photonic elements. Moreover the efficient spin-photon interface provided by self-assembled quantum dots[1] allows us to reach an unprecedented rate of 2300 entangled spin pairs per second, which represents an improvement of four orders of magnitude as compared to prior experiments[2]. The entanglement generation scheme relies on single photon interference of Raman scattered light from both dots[3]. A single photon detection projects the system into a maximally entangled state. We developed a delayed two-photon interference scheme that allows for efficient verification of quantum correlations. Our results lay the groundwork for the realization of quantum repeaters and quantum networks on a chip. [1] W.-B. Gao et al., Nature 491, 426 (2012) [2] L. Slodicka et al., Phys. Rev. Lett. 110, 083603 (2013) [3] C. Cabrillo et al. Phys. Rev. A 59, 1025 (1999) -1 0 1 2 3 4 5 6 7 8 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 data sine fit ra ti o pulse duration (arb. u.) F x = 29.8 ± 2.6 % 180 min 0.13 /s 0 19 37 56 74 93 112 0.0 0.1 0.2 0.3 0.4 0.5 0.6 total fidelity = 55.2 ± 3.5 % F Z = 80.6 ± 6.6 % c o in c id e n c e s / 1 0 6 .5 h measurement coincidences ideal case

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Entanglement plays a central role in fundamental tests of quantum mechanics as well as in the burgeoning field of quantum information processing. Particularly in the context of quantum networks and communication, a major challenge is the efficient generation of entanglement between distant stationary (spin) qubits. Here, we report the realization of heralded quantum entanglement between two semiconductor quantum dot spins separated by more than five meters. Our results extend the previous demonstrations of distant spin entanglement in single trapped ions or neutral atoms, in atom ensembles and nitrogen vacancy centers to the domain of artificial atoms in semiconductor nanostructures that allow for onchip integration of electronic and photonic elements. Moreover the efficient spin-photon interface provided by self-assembled quantum dots[1] allows us to reach an unprecedented rate of 2300 entangled spin pairs per second, which represents an improvement of four orders of magnitude as compared to prior experiments[2]. The entanglement generation scheme relies on single photon interference of Raman scattered light from both dots[3]. A single photon detection projects the system into a maximally entangled state. We developed a delayed two-photon interference scheme that allows for efficient verification of quantum correlations. Our results lay the groundwork for the realization of quantum repeaters and quantum networks on a chip. [1] W.-B. Gao et al., Nature 491, 426 (2012) [2] L. Slodicka et al., Phys. Rev. Lett. 110, 083603 (2013) [3] C. Cabrillo et al. Phys. Rev. A 59, 1025 (1999) -1 0 1 2 3 4 5 6 7 8 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 data sine fit ra ti o pulse duration (arb. u.) F x = 29.8 ± 2.6 % 180 min 0.13 /s 0 19 37 56 74 93 112 0.0 0.1 0.2 0.3 0.4 0.5 0.6 total fidelity = 55.2 ± 3.5 % F Z = 80.6 ± 6.6 % c o in c id e n c e s / 1 0 6 .5 h measurement coincidences ideal case
Quantum entanglement emerges naturally in interacting quantum systems and plays a central role in quantum information processing. Remarkably, it is possible to generate entanglement even in the absence of direct interactions: provided that which path information is erased, weak spin-state dependent light scattering can be used to project two distant spins onto a maximally entangled state upon detection of a single photon. Even though this approach is necessarily probabilistic, successful generation of entanglement is heralded by the photon detection event. Here, we demonstrate heralded quantum entanglement of two quantum dot heavy-hole spins separated by 5 meters using single-photon interference. Thanks to the long coherence time of hole spins and the efficient spin-photon interface provided by self-assembled quantum dots embedded in leaky microcavity structures, we generate 2300 entangled spin pairs per second, which represents an improvement approaching three orders of magnitude as compared to prior experiments. Delayed two-photon interference scheme we developed allows for efficient verification of quantum correlations. Our results lay the groundwork for the realization of quantum networks in semiconductor nanostructures. Combined with schemes for transferring quantum information to a long-lived memory qubit, fast entanglement generation we demonstrate could also impact quantum repeater architectures.
Self-assembled quantum dots can act as an interface between single spins and photons. They combine the flexibility and scalability of semiconductor systems with near-perfect two level systems, emitting highly coherent single photons. In potential quantum information processing architectures based upon optical networks, quantum dots permit light-matter coupling between matter qubits and photonic links. Single trapped charge carriers in quantum dots can be addressed optically, generating spin-photon entanglement between the matter qubits and \lq flying' photon qubits, a key first step in creation of a network. Such an optically linked network of spins in quantum dots has yet to be realized. The semiconductor environment presents a key challenge; it broadens the spectrum of the emitted light, which reduces the fidelity of schemes based upon photon exchange or interference. In addition, these quantum dots are subject to hyperfine coupling to a bath of >>> 105^{5}5 nuclear spins. While this presents an opportunity to study the physics of a central spin in a spin bath, it degrades the spin coherence of a trapped electron or hole. The suggested gate operations to generate entanglement, and the spin measurements to verify a created state, rely upon photon detection. Thus a second limitation occurs due to low efficiency of detectors and photon collection probability. Recent developments in detector technology have enabled us to bring generation and verification of entangled states with quantum dots into the realm of possibility. This dissertation begins with a detailed study of the interaction of a single electron spin with the solid state environment of the quantum dot, analysing the intensity noise of scattered light under resonant excitation to uncover the timescales and relative amplitudes of identified noise sources. A technique for rapid characterization of samples is presented, focusing in particular upon comparison of spectral broadening of the optical transitions relevant to a spin-photon interface. Having identified the extent of environmental factors acting upon the quantum dots, we turn to a demonstration of photon-mediated entanglement between two distant electron spins using a probabilistic scheme. We are able to generate entangled states at 7 kHz, the fastest yet reported for photon-mediated protocols. The average state fidelity of the created Bell states is 63.5 ±\pm± 3.0 \%., violating the classical limit by over 4 standard deviations of the mean. In addition, we demonstrate full optical phase tuning of the Bell state ∣Ψ=12(∣↑∣↓+eiϕ∣↓∣↑)|{\Psi} = \frac{1}{\sqrt{2}}\left(|{\uparrow}|{\downarrow} + e^{i\phi}|{\downarrow}|{\uparrow} \right)∣Ψ=2​1​(∣↑∣↓+eiϕ∣↓∣↑). This is a proof of principle experiment, and sets a fidelity benchmark upon which gains can be made by mitigation of environmental dynamics.
Entanglement plays a central role in fundamental tests of quantum mechanics as well as in the burgeoning field of quantum information processing. Particularly in the context of quantum networks and communication, an outstanding challenge is the efficient generation of entanglement between stationary (spin) and flying (photon) qubits. In this talk, I will first show the observation of quantum entanglement between a semiconductor quantum dot spin and the color of a propagating optical photon [1]. The demonstration of entanglement relies on the use of fast single-photon detection which allows us to project the photon into a superposition of its two frequency components. Our results extend the previous demonstrations of single-spin-photon entanglement in trapped ions, neutral atoms and nitrogen vacancy centers to the domain of artificial atoms in semiconductor nano-structures that allow for integration of electronic and photonic elements.
Entanglement plays a central role in fundamental tests of quantum mechanics as well as in the burgeoning field of quantum information processing. Particularly in the context of quantum networks and communication, a major challenge is the efficient generation of entanglement between stationary (spin) and flying (photon) qubits. Here we report the observation of quantum entanglement between a semiconductor quantum dot spin and the color of a propagating optical photon. As an extension experiment, we report the generation of a single-photon frequency qubit, interference of resonance fluorescence from two distant quantum dots and the teleportation from a flying photon to a quantum dot spin.
Quantum entanglement between distant qubits is an important feature of quantum networks. Distribution of entanglement over long distances can be enabled through coherently interfacing qubit pairs via photonic channels. Here, we report the realization of optically generated quantum entanglement between electron spin qubits confined in two distant semiconductor quantum dots. The protocol relies on spin-photon entanglement in the trionic Λ system and quantum erasure of the Raman-photon path information. The measurement of a single Raman photon is used to project the spin qubits into a joint quantum state with an interferometrically stabilized and tunable relative phase. We report an average Bell-state fidelity for |ψ^{(+)}⟩ and |ψ^{(-)}⟩ states of 61.6±2.3% and a record-high entanglement generation rate of 7.3 kHz between distant qubits.
Abstract The realization of on-chip quantum interfaces between flying photons and solid-state spins is a key building block for quantum-information processors, enabling, e.g., distributed quantum computing, where remote quantum registers are interconnected by flying photons. Self-assembled quantum dots integrated into nanostructures are one of the most promising systems for such an endeavor thanks to their near-unity photon-emitter coupling and fast spontaneous emission rate. Here we demonstrate high-fidelity on-chip entanglement between an incoming photon and a stationary quantum-dot hole spin qubit. The entanglement is induced by sequential scattering of the time-bin encoded photon interleaved with active spin control within a microsecond, two orders of magnitude faster than those achieved in other solid-state platforms. Conditioning on the detection of a reflected photon renders the entanglement fidelity immune to the spectral wandering of the emitter. These results represent a major step towards realizing a quantum node capable of interchanging information with flying photons and on-chip quantum logic, as required for quantum networks and quantum repeaters.