Compared to classical light sources, quantum sources based on N00N states consisting of N photons achieve an N-times higher phase sensitivity, giving rise to super-resolution.1, 2, 3 N00N-state creation schemes based on linear optics and projective measurements only have a success probability p that decreases exponentially with N,4, 5, 6 e.g. p = 4.4x10-14 for N = 20.7 Feed-forward improves the scaling but N fluctuates nondeterministically in each attempt.8, 9 Schemes based on parametric down-conversion suffer from low production efficiency and low fidelity.9 A recent scheme based on atoms in a cavity combines deterministic time evolution, local unitary operations, and projective measurements.10 Here we propose a novel scheme based on the off-resonant interaction of N photons with four semiconductor quantum dots (QDs) in a cavity to create GHZ states, also called polarization N00N states, deterministically with p = 1 and fidelity above 90% for N≤ 60, without the need of any projective measurement or local unitary operation. Using our measure we obtain maximum N-photon entanglement EN = 1 for arbitrary N. Our method paves the way to the miniaturization of N00N and GHZ-state sources to the nanoscale regime, with the possibility to integrate them on a computer chip based on semiconductor materials.
Compared to classical light sources, quantum sources based on N00N states consisting of N photons achieve an N-times higher phase sensitivity, giving rise to super-resolution.1, 2, 3 N00N-state creation schemes based on linear optics and projective measurements only have a success probability p that decreases exponentially with N,4, 5, 6 e.g. p = 4.4x10-14 for N = 20.7 Feed-forward improves the scaling but N fluctuates nondeterministically in each attempt.8, 9 Schemes based on parametric down-conversion suffer from low production efficiency and low fidelity.9 A recent scheme based on atoms in a cavity combines deterministic time evolution, local unitary operations, and projective measurements.10 Here we propose a novel scheme based on the off-resonant interaction of N photons with four semiconductor quantum dots (QDs) in a cavity to create GHZ states, also called polarization N00N states, deterministically with p = 1 and fidelity above 90% for N≤ 60, without the need of any projective measurement or local unitary operation. Using our measure we obtain maximum N-photon entanglement EN = 1 for arbitrary N. Our method paves the way to the miniaturization of N00N and GHZ-state sources to the nanoscale regime, with the possibility to integrate them on a computer chip based on semiconductor materials.
Compared to classical light sources, quantum sources based on N00N states consisting of N photons achieve an N-times higher phase sensitivity, giving rise to super-resolution. N00N-state creation schemes based on linear optics and projective measurements only have a success probability p that decreases exponentially with N, e.g. p=4.4×10−14 for N=20. Feed-forward improves the scaling but N fluctuates nondeterministically in each attempt. Schemes based on parametric down-conversion suffer from low production efficiency and low fidelity. A recent scheme based on atoms in a cavity combines deterministic time evolution, local unitary operations, and projective measurements. Here we propose a novel scheme based on the off-resonant interaction of N photons with four semiconductor quantum dots (QDs) in a cavity to create N00N states deterministically with p=1 and fidelity above 90% for N≲60, without the need of any projective measurement or local unitary operation. Using our measure we obtain maximum N-photon entanglement EN=1 for arbitrary N. Our method paves the way to the miniaturization of N00N-state sources to the nanoscale regime, with the possibility to integrate them on a computer chip based on semiconductor materials.
Abstract We present a deterministic scheme for generating large scale GHZ states in a cavity-quantum dot system. A singly charged quantum dot is embedded in a double-sided optical microcavity with partially reflective top and bottom mirrors. The GHZ-type Bell spin state can be created and two n -spin GHZ states can be perfectly fused to a 2 n -spin GHZ state with the help of n ancilla single-photon pulses. The implementation of the current scheme only depends on the photon detection and its need not to operate multi-qubit gates and multi-qubit measurements. Discussions about the effect of the cavity loss, side leakage and exciton cavity coupling strength for the fidelity of generated states show that the fidelity can remain high enough by controlling system parameters. So the current scheme is simple and feasible in experiment.
Quantum technologies witness rapid contemporary developments transitioning from abstract scientific ideas and fundamental demonstrations, into systems of sufficient quality and scale, enabling real applications. Photonic quantum technologies are playing a pivotal role in these developments, since photons are robust, easily controlled, detect and measured, thus qualify as flying carriers of quantum information and entanglement distributers. The efforts to develop photonic quantum technologies benefit from the maturity of the classical optical technologies. It was shown that even a source of heralded three entangled photons is sufficient for building large scale quantum computers using otherwise classical optical elements. Here, we demonstrate a novel semiconductor quantum dot based device, which deterministically generate at GHz rates, indistinguishable single photons in a robust Greenberger-Horne-Zeilinger (GHZ) state of more than a dozen photons. The device utilizes novel natural spin echo concept, provided by the opposite precession directions of the negative and positive carriers' spins in the excited and ground levels of the periodically excited dot, respectively. The excitation rate is finely tuned to nullify the phase acquired by both spins' precession. Our record long GHZ state producing device can yet be feasibly improved to provide higher-rate, brighter and more robust deterministic GHZ source, significantly reducing the overhead requirements for photonic quantum technologies.
Photonic graph states are underlying resources for one-way optical quantum computation, quantum error correction, fundamental testing of quantum mechanics, and quantum communication networks. Most existing works, however, are based on the spontaneous parametric down-conversion sources that intrinsically suffer from probabilistic generation and double pair components. Here, we create two important classes of graph states, a polarization-encoded four-photon Greenberger–Horne–Zeilinger (GHZ) state and a linear cluster state, by actively demultiplexing a deterministic single-photon source from a semiconductor quantum dot embedded in a micropillar. A state fidelity of 0.790 ± 0.009 (0.763 ± 0.004) and a count rate of ∼13 Hz are observed for the four-photon GHZ (cluster) state. The results constitute a new route toward the multiphoton entanglement with deterministic single-photon sources.
Multi-photon entangled states such as `N00N states' have attracted a lot of attention because of their possible application in high-precision phase measurements. So far, N00N states have been generated by spontaneous parametric down-conversion sources and by mixing quantum and classical light on a beam splitter. However, single-photon on demand sources promise to be more efficient and scalable than down-conversion sources which are probabilistic in nature. Here, we demonstrate super-resolving phase measurements based on two-photon N00N states generated by a quantum dot single-photon source utilizing the Hong-Ou-Mandel effect on a beam splitter. The quantum dot was excited through a two-photon resonant excitation scheme. Using a π-pulse, this results in the deterministic generation of indistinguishable single photons from both, the biexciton and exciton radiative recombination processes. Launching either type of the photons into both inputs of an interferometer, phase super-resolution, i.e. an interference fringe spacing with doubled rate relative to the single photon rate has been observed for both transitions. Interference visibilities of VN=2,XX=0.54±0.01 for the biexciton and VN=2,X=0.46±0.02 for the exciton transition have been obtained, respectively.
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 .