Quantum Beat of Two Single Photons

Legero, Thomas; Wilk, Tatjana; Hennrich, Markus; Rempe, Gerhard; Kuhn, Axel

doi:10.1103/physrevlett.93.070503

Cited by 272 publications

(338 citation statements)

References 17 publications

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“…For δτ = 50 ns the correlation function G (2) ab (τ ) remains close to zero at τ = 0, indicating the coalescence of those photons detected with a vanishingly small time difference 6,25,26 (see Fig. 2d).…”

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confidence: 98%

Correlations, indistinguishability and entanglement in Hong–Ou–Mandel experiments at microwave frequencies

et al. 2013

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When two indistinguishable single photons impinge at the two inputs of a beam splitter they coalesce into a pair of photons appearing in either one of its two outputs. This effect is due to the bosonic nature of photons and was first experimentally observed by Hong, Ou and Mandel 1 . Here, we present the observation of the Hong-Ou-Mandel effect with two independent single-photon sources in the microwave frequency domain. We probe the indistinguishability of single photons, created with a controllable delay, in time-resolved secondorder cross-and auto-correlation function measurements. Using quadrature amplitude detection we are able to resolve different photon numbers and detect coherence in and between the output arms. This scheme allows us to fully characterize the two-mode entanglement of the spatially separated beam-splitter output modes. Our experiments constitute a first step towards using two-photon interference at microwave frequencies for quantum communication and information processing 2-5 .So far, Hong-Ou-Mandel (HOM) two-photon interference has been demonstrated exclusively using photons at optical or telecom wavelengths. Experiments were performed with photons emitted from a single source using parametric downconversion 1 , trapped ions 3 , atoms 6 , quantum dots 7 and single molecules 8 . The HOM effect has also been observed with two independent sources 9-15 realizing indistinguishable single-photon states, which are required as a resource in quantum networks or linear-optics quantum computation. Such experiments have also been performed using donor impurities as sources 16 including nitrogen-vacancy centres in diamond (see ref. 17 and references therein). Furthermore, the HOM effect has been employed to create entanglement between ions 18 in spatially separated traps, and to realize a controlled-NOT gate in a small-scale photonic network 19 . Similar physics is also actively explored with ballistic electrons in solids (see ref. 20 and references therein).Here, we demonstrate the HOM interference of two indistinguishable microwave photons emitted from independent triggered sources realized in superconducting circuits (see Methods). The photons are prepared in two separate microwave resonators A (B) using transmon-type qubits and decay exponentially at rates κ/2π = 4.1 (4.6) MHz through their strongly coupled output ports into the input modesâ andb of the beam splitter (see Fig. 1). The two photons then interfere at the beam splitter and are emitted into the output modesâ andb (see Fig. 1a). Using the dispersive interaction between qubit and resonator, we tune the emission frequencies of the two sources to an identical value of ν r = 7.2506 GHz. For our experiments, we sequentially create 20 single photons in each source at a rate 1/t r = 1/512 ns ∼ 1.95 MHz in a sequence repeated every 12.5 µs.To probe the photon statistics in the beam-splitter output modesâ andb we use two spatially separated heterodyne detection channels 21,22 (see dashed rectangle in Fig. 1b). Each channel consists of a set of...

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confidence: 98%

Correlations, indistinguishability and entanglement in Hong–Ou–Mandel experiments at microwave frequencies

et al. 2013

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“…Similarly, the oscillations in Fig. 4g come from a two-photon interference between a photon at |o r S À |o b S and the second one either at |o r S þ |o b S (Period 0) or a completely mixed state (Period 1) 39 .…”

Section: Indistinguishable Photonic Frequency Qubitsmentioning

confidence: 99%

“…For any given arrival time at the beam splitter, such a delay ensures that the relative phase between the two frequency components of the two single photons differs by p. The observed beat notes around the centre period near zero delay time, stem from an interference between the two frequency qubits ð1= ffiffi ffi 2 p Þðj o b i þ e iy j o r iÞ and ð1= ffiffi ffi 2 p Þð j o b i À e iy j o r iÞ; a similar beat note would be observed for input photons in |o b S and |o r S (ref. 39). The suppression of the beat signal in different periods in this case stems from a superposition of two p-phase-shifted single-photon interference patterns.…”

Section: Indistinguishable Photonic Frequency Qubitsmentioning

confidence: 99%

Quantum teleportation from a propagating photon to a solid-state spin qubit

et al. 2013

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A quantum interface between a propagating photon used to transmit quantum information and a long-lived qubit used for storage is of central interest in quantum information science. A method for implementing such an interface between dissimilar qubits is quantum teleportation. Here we experimentally demonstrate transfer of quantum information carried by a photon to a semiconductor spin using quantum teleportation. In our experiment, a single photon in a superposition state is generated using resonant excitation of a neutral dot. To teleport this photonic qubit, we generate an entangled spin-photon state in a second dot located 5 m away and interfere the photons from the two dots in a Hong-Ou-Mandel set-up. Thanks to an unprecedented degree of photon-indistinguishability, a coincidence detection at the output of the interferometer heralds successful teleportation, which we verify by measuring the resulting spin state after prolonging its coherence time by optical spin-echo.

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“…The interferometers erase the time information and temporally distinguishable events (at t and t + τ respectively) interfere 10,13,22 . Changing the relative phase α − β between the interferometers leads to interference fringes in the coincidence count rates.…”

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Entangling independent photons by time measurement

et al. 2007

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Entanglement is at the heart of quantum physics, both for its conceptual foundations and for applications in quantum communication. Remarkably, entanglement can be 'swapped': if we prepare two independent entangled pairs A1-A2 and B1-B2, a joint measurement on A1 and B1 (called a 'Bellstate measurement', BSM) has the effect of projecting A2 and B2 onto an entangled state, although these two particles have never interacted nor share any common past 1,2 . Entanglement swapping with photon pairs has already been experimentally demonstrated 3-6 using pulsed sources-where the challenge was to achieve sufficiently sharp synchronization of the photons in the BSM-but never with continuous-wave sources, as originally proposed 2 . Here, we present an experiment where the coherence time of the photons exceeds the temporal resolution of the detectors. Hence, photon timing can be obtained by the detection times, and pulsed sources can be replaced by continuous-wave sources, which do not require any synchronization 6,7 . This allows for the first time the use of completely autonomous sources, an important step towards real-world quantum networks with truly independent and distant nodes.The BSM is the essential element in an entanglement-swapping experiment. Linear optics allows the realization of only a partial BSM 8 by coupling the two incoming modes on a beam splitter and observing a suitable detection pattern in the outgoing modes. Such a measurement is successful in at most 50% of the cases. Still, a successful partial BSM entangles two photons that were, up to then, independent. The physics behind this realization is the bosonic character of photons. It is therefore crucial that the two incoming photons are indistinguishable: they must be identical in their spectral, spatial, polarization and temporal modes at the beam splitter; spectral overlap is achieved by the use of similar filters, spatial overlap by the use of single-mode optical fibres and polarization is matched by a polarization controller. In addition, the temporal resolution must be unambiguous: detection at a time t ± t d , where t d is the temporal resolution of the detector, must single out a unique time mode. In previous experiments, synchronized pulsed sources created both of the photons at the same time and path lengths had to be matched to obtain the required temporal overlap. The pulse length, that is, the coherence length of the photons, was τ c t d (typically τ c < 1 ps), but two subsequent pulses were separated by more than t d (ref. 9). The drawback of such a realization is that the two sources cannot be totally autonomous, because of the indispensable synchronization. For the case where τ c > t d (ref. 10), the detectors always single out a unique time mode. As a benefit, we can give up the pulsed character of the sources and the synchronization between them. By implementing this, we realize for the first time the entanglement swapping scheme as originally proposed in ref. 2.The experimental scheme is shown in Fig. 1. Each of the two nonlinear cr...

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Quantum Beat of Two Single Photons

Cited by 272 publications

References 17 publications

Correlations, indistinguishability and entanglement in Hong–Ou–Mandel experiments at microwave frequencies

Correlations, indistinguishability and entanglement in Hong–Ou–Mandel experiments at microwave frequencies

Quantum teleportation from a propagating photon to a solid-state spin qubit

Entangling independent photons by time measurement

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