Scalable performance in solid-state single-photon sources

Abstract

The desiderata for an ideal photon source are high brightness, high single-photon purity, and high indistinguishability. Defining brightness at the first collection lens, these properties have been simultaneously demonstrated with solid-state sources, however absolute source efficiencies remain close to the 1% level, and indistinguishability only demonstrated for photons emitted consecutively on the few nanosecond scale. Here we employ deterministic quantum dot-micropillar devices to demonstrate solid-state single-photon sources with scalable performance. In one device, an absolute brightness at the output of a single-mode fibre of 14% and purities of 97.1-99.0% are demonstrated. When non-resontantly excited, it emits a long stream of photons that exhibit indistinguishability up to 70%-above the classical limit of 50%-even after 33 consecutively emitted photons, a 400 ns separation between them. Resonant excitation in other devices results in near-optimal indistinguishability values: 96% at short timescales, remaining at 88% in timescales as large as 463 ns, after 39 emitted photons. The performance attained by our devices brings solid-state sources into a regime suitable for scalable implementations.Photon indistinguishability-responsible for unique quantum phenomena with no classical counterpart, notably photon bunching via interference [1]-has been demonstrated in various physical systems [2][3][4][5][6][7][8][9], resulting in a broad range of applications in photonic quantum technologies [10], including quantum teleportation [11,12], generation of entangled photon sources [13][14][15], and linear-optics quantum computation [16,17]. However, achieving conclusive indistinguishability, i..e. above 50% (the classical limit), while simultaneously displaying high single-photon purity and high absolute brightness is experimentally challenging.Semiconductor quantum dots (QDs) inserted in photonic structures [18][19][20][21][22] are a rapidly improving technology for generating bright sources of indistinguishable single-photons. Addressing the excited states of the quantum dot using a non-resonant scheme early showed two-photon interference visibilities in the 70%−80% range [8], yet with limited collection efficiencies. Improvements in the efficiency have been made by deterministically placing the quantum dot in the centre of a photonic micro-cavity. Here the acceleration of photon emission into well defined cavity modes [23], due to Purcell enhancement, has enabled two-photon interference visibilities in the same range, with simultaneous efficiencies at the first collection lens around 80% [9]. Near-unity indistinguishability, in turn, has been achieved in recent years under strictly-resonant excitation of the quantum dot [24][25][26], whereas the recent development of electric control on deterministically coupled devices [27]-thus with scalable fabrication-has now enabled strictlyresonant excitation in combination with Purcell enhancement, resulting in near-optimal single-photon sources [28] with visibilities reach...

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