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Physical Review Letters

Quantum-Dot Single-Photon Sources for Entanglement Enhanced Interferometry

Markus A. Müller, Hüseyin Avni Vural, Christian Schneider, Armando Rastelli, Oliver G. Schmidt, Sven Höfling, Peter Michler

Published Jun 22, 2017• 74 citations
Publisher

Abstract

Multiphoton entangled states such as "N00N states" have attracted a lot of attention because of their possible application in high-precision, quantum enhanced phase determination. So far, N00N states have been generated in spontaneous parametric down-conversion processes and by mixing quantum and classical light on a beam splitter. Here, in contrast, we demonstrate superresolving phase measurements based on two-photon N00N states generated by quantum dot single-photon sources making use of the Hong-Ou-Mandel effect on a beam splitter. By means of pulsed resonance fluorescence of a charged exciton state, we achieve, in postselection, a quantum enhanced improvement of the precision in phase uncertainty, higher than prescribed by the standard quantum limit. An analytical description of the measurement scheme is provided, reflecting requirements, capability, and restraints of single-photon emitters in optical quantum metrology. Our results point toward the realization of a real-world quantum sensor in the near future.

DOI
10.1103/physrevlett.118.257402

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Multiphoton entangled states such as "N00N states" have attracted a lot of attention because of their possible application in high-precision, quantum enhanced phase determination. So far, N00N states have been generated in spontaneous parametric down-conversion processes and by mixing quantum and classical light on a beam splitter. Here, in contrast, we demonstrate superresolving phase measurements based on two-photon N00N states generated by quantum dot single-photon sources making use of the Hong-Ou-Mandel effect on a beam splitter. By means of pulsed resonance fluorescence of a charged exciton state, we achieve, in postselection, a quantum enhanced improvement of the precision in phase uncertainty, higher than prescribed by the standard quantum limit. An analytical description of the measurement scheme is provided, reflecting requirements, capability, and restraints of single-photon emitters in optical quantum metrology. Our results point toward the realization of a real-world quantum sensor in the near future.
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 πππ-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±0.01V_{N=2,\mathit{XX}}=0.54\pm0.01VN=2,XX​=0.54±0.01 for the biexciton and VN=2,X=0.46±0.02V_{N=2,\mathit{X}}=0.46\pm0.02VN=2,X​=0.46±0.02 for the exciton transition have been obtained, respectively.
In principle, the use of entangled photons provides enhanced precision in optical phase measurements. This precision significantly surpasses the classical shot-noise limit, and thereby has many possible applications in science and technology. In practice, however, entangled multiphoton states have been generated so far using various intrinsically probabilistic and unscalable processes, thereby counteracting the advantages that the entangled photon states might have. The authors overcome these limitations here by using a quantum knitting machine, based on a single semiconductor quantum dot, to generate a polarization-entangled multiphoton state in a deterministic manner. The multiphoton state is then used to demonstrate super-sensitive optical phase measurement. The results pave the way for realizing genuine quantum enhanced optical measurements in the very near future.
The quantum statistical fluctuations of electromagnetic fields establish a limit, known as the shot-noise limit, on the sensitivity of optical measurements performed with classical technologies. However, quantum technologies are not constrained by this shot-noise limit. In this regard, the possibility of using every photon produced by quantum sources of light to estimate small physical parameters, beyond the shot-noise limit, constitutes one of the main goals of quantum optics. Here, we experimentally demonstrate a scalable protocol for quantum-enhanced optical phase estimation across a broad range of phases, with neither pre- nor post-selected measurements. This is achieved through the efficient design of a source of spontaneous parametric downconversion in combination with photon-number-resolving detection. The robustness of two-mode squeezed vacuum states against loss allows us to outperform schemes based on N00N states, in which the loss of a single photon is enough to remove all phase information from a quantum state. In contrast to other schemes that rely on N00N states or conditional measurements, the sensitivity of our technique could be improved through the generation and detection of high-order photon pairs. This unique feature of our protocol makes it scalable. Our work is important for quantum technologies that rely on multiphoton interference such as quantum imaging, boson sampling, and quantum networks.
Quantum metrology can achieve enhanced sensitivity for estimating unknown parameters beyond the standard quantum limit. Recently, multiple-phase estimation exploiting quantum resources has attracted intensive interest for its applications in quantum imaging and sensor networks. For multiple-phase estimation, the amount of enhanced sensitivity is dependent on quantum probe states, and multi-mode N00N states are known to be a key resource for this. However, its experimental demonstration has been missing so far since generating such states is highly challenging. Here, we report generation of multi-mode N00N states and experimental demonstration of quantum enhanced multiple-phase estimation using the multi-mode N00N states. In particular, we show that the quantum Cramer-Rao bound can be saturated using our two-photon four-mode N00N state and measurement scheme using a 4 × 4 multi-mode beam splitter. Our multiple-phase estimation strategy provides a faithful platform to investigate multiple parameter estimation scenarios.
While two-photon Hong-Ou-Mandel interference visibility has become a standard metric for single-photon sources, many optical quantum technologies require the generation and manipulation of larger photonic states. To date, efficiency limitations have prevented scaling quantum dot-based interference to the coalescence of more than two photons at a single beamsplitter. We overcome this limitation by combining a state-of-the-art quantum dot source with deterministic demultiplexing, enabling the direct observation of quantum interference fringes arising from up to four photons. We measure high mean interference contrasts of 93.0±0.1 %93.0 \pm 0.1~\%93.0±0.1 % for two photons, and 84.1±1.0 %84.1 \pm 1.0~\%84.1±1.0 % for four photons, with the complex fringe structure fully reproduced by a theoretical model. These results reveal the existence of "deep fringes" whose minima are unaffected by distinguishable photons, rendering the maximum contrast of four-photon interference highly sensitive to multi-photon emission but robust against photon distinguishability. We predict that these phenomena will extend to interference of larger numbers of photons, with relevance across a range of potential optical quantum technologies. A Fisher information analysis demonstrates that interference fringes from our source can exhibit phase sensitivity beyond the standard quantum limit, illustrating potential applications in quantum metrology.
Abstract Single-photon sources based on semiconductor quantum dots find several applications in quantum information processing due to their high single-photon indistinguishability, on-demand generation, and low multiphoton emission. In this context, the generation of entangled photons represents a challenging task with a possible solution relying on the interference in probabilistic gates of identical photons emitted at different pulses from the same source. In this work, we implement this approach via a simple and compact design that generates entangled photon pairs in the polarization degree of freedom. We operate the proposed platform with single photons produced through two different pumping schemes, the resonant excited one and the longitudinal-acoustic phonon-assisted configuration. We then characterize the produced entangled two-photon states by developing a complete model taking into account relevant experimental parameters, such as the second-order correlation function, Hong–Ou–Mandel visibility, multiphoton emission and pump laser filtering. Our source shows long-term stability and high quality of the generated entangled states, thus constituting a reliable building block for optical quantum technologies.