Purification of a single-photon nonlinearity

H Snijders,E C Langman,D Bouwmeester,J E Bowers,M P Van Exter,M P Bakker,W Löffler,J A Frey,A Gossard,J Norman

doi:10.1038/ncomms12578

H Snijders, E C Langman + Show 8 more

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https://doi.org/10.1038/ncomms12578

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Single photon nonlinearities based on a semiconductor quantum dot in an optical microcavity are a promising candidate for integrated optical quantum information processing nodes. In practice, however, the finite quantum dot lifetime and cavity-quantum dot coupling lead to reduced fidelity. Here we show that, with a nearly polarization degenerate microcavity in the weak coupling regime, polarization pre- and postselection can be used to restore high fidelity. The two orthogonally polarized transmission amplitudes interfere at the output polarizer; for special polarization angles, which depend only on the device cooperativity, this enables cancellation of light that did not interact with the quantum dot. With this, we can transform incident coherent light into a stream of strongly correlated photons with a second-order correlation value up to 40, larger than previous experimental results, even in the strong-coupling regime. This purification technique might also be useful to improve the fidelity of quantum dot based logic gates.

Highlights

Single photon nonlinearities based on a semiconductor quantum dot in an optical microcavity are a promising candidate for integrated optical quantum information processing nodes
Our device consists of self-assembled InAs/GaAs quantum dot (QD) embedded in a micropillar Fabry–Perot cavity grown by molecular beam epitaxy[25]
We have shown by experiment and theory that the reduced fidelity of a QD nonlinearity, caused by imperfect QD-cavity coupling, can be strongly enhanced by pre- and post-selection of specific polarization states

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Introduction

Single photon nonlinearities based on a semiconductor quantum dot in an optical microcavity are a promising candidate for integrated optical quantum information processing nodes. We show, using a nearly polarization-degenerate cavity in the weak coupling CQED regime, that we can transform incident coherent light into a stream of strongly correlated photons with g2(0) 1⁄4 25.7±0.9, corresponding to \40 in the absence of detector jitter. The polarization-degenerate cavity enables us to choose the incident polarization yin 1⁄4 45° such that both fine-structure split QD transitions along yXQD 1⁄4 0 and yYQD 1⁄4 90 are excited, and we can use a postselection polarizer behind the cavity (yout) to induce quantum interference of the two transmitted orthogonal polarization components (Fig. 1a).

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