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arXiv:2010.05570 · Physical review. B./Physical review. B

Delaying two-photon Fock states in hot cesium vapor using single photons generated on demand from a semiconductor quantum dot

Hüseyin Avni Vural, Simon Seyfferle, Ilja Gerhardt, Michael Jetter, Simone Luca Portalupi, Peter Michler

Published May 5, 2021• 3 citations
arXivHTMLPDF

Abstract

Single photons from solid-state quantum emitters are playing a crucial role in the development of photonic quantum technologies and, by extension, higher order states, such as N-photon Fock states, allow for applications, e.g., in quantum-enhanced sensing. To verify the applicability of these states in future quantum technological implementations involving photon-atom interactions (i.e., storage of a quantum state in alkali vapor and photon delay) we utilize in the present study the dispersion of a hot cesium vapor at the ${D}_{1}$ line to realize a temporal delay for two-photon Fock states as a result of the slow-light effect. Single photons are generated on demand from an InGaAs quantum dot, while their quantum interference at a beam splitter is used to generate a two-photon Fock state. We verify the successful propagation and the preservation of the two-photon Fock states after the interaction with the slow-light medium, while a significant temporal delay (five times the initial photon length) is achieved with a high vapor transmission of $90%$.

DOI
10.1103/physrevb.103.195304

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In forthcoming quantum networks various quantum systems might be involved to accomplish individual tasks, including storage of quantum states, quantum logic operations, error correction, or entanglement distillation. An interface between a single photon emitter and a potential photon storage could provide one fundamental building block of such a hybrid quantum system. Semiconductor quantum dots (QD) and atomic vapors have already been brought together by single photon spectroscopy of cesium and rubidium [1,2], narrow filtering of QD resonance fluorescence in cesium [3], slowing down QD photons by dispersion between the 6.8 GHz hyperfine-split rubidium D2transitions [4] and in the middle of the four cesium D1 transitions [5] (at around 5.0 GHz in Fig. 1 b).In our experiment the neutrally charged excitonic transition of a strain-tunable InGaAs QD is pumped either resonantly or non-resonantly by a pulsed laser. The QD emission is set between two cesium D1 transitions at 894 nm, which are hyperfine-split only by 1.2 GHz, with a very strong dispersion compared to preceding studies [4,5]. This allows for delay times of a few nanoseconds even at low optical densities, resulting in a propagation velocity at the order of 1/20 of the vacuum speed of light. Such a single photon - atom interface might lay the foundations for a low-loss quantum memory in a future hybrid quantum network.
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Hybrid interfaces between distinct quantum systems play a major role in the implementation of quantum networks. Quantum states have to be stored in memories to synchronize the photon arrival times for entanglement swapping by projective measurements in quantum repeaters or for entanglement purification. Here, we analyze the distortion of a single-photon wave packet propagating through a dispersive and absorptive medium with high spectral resolution. Single photons are generated from a single In(Ga)As quantum dot with its excitonic transition precisely set relative to the Cesium D1 transition. The delay of spectral components of the single-photon wave packet with almost Fourier-limited width is investigated in detail with a 200 MHz narrow-band monolithic Fabry-Pérot resonator. Reflecting the excited state hyperfine structure of Cesium, “slow light” and “fast light” behavior is observed. As a step towards room-temperature alkali vapor memories, quantum dot photons are delayed for 5 ns by strong dispersion between the two 1.17 GHz hyperfine-split excited state transitions. Based on optical pumping on the hyperfine-split ground states, we propose a simple, all-optically controllable delay for synchronization of heralded narrow-band photons in a quantum network.
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