Frequency stabilization of the zero-phonon line of a quantum dot via phonon-assisted active feedback

Abstract

We report on the feedback stabilization of the zero-phonon emission frequency of a single InAs quantum dot. The spectral separation of the phonon-assisted component of the resonance fluorescence provides a probe of the detuning between the zero-phonon transition and the resonant driving laser. Using this probe in combination with active feedback, we stabilize the zero-phonon transition frequency against environmental fluctuations. This protocol reduces the zero-phonon fluorescence intensity noise by a factor of 22 by correcting for environmental noise with a bandwidth of 191 Hz, limited by the experimental collection efficiency. The associated sub-Hz fluctuations in the zerophonon central frequency are reduced by a factor of 7. This technique provides a means of stabilizing the quantum dot emission frequency without requiring access to the zero-phonon emission.A robust single photon source is an integral component for the implementation of many quantum technologies including linear optical quantum computing [1,2], quantum relays [3], and quantum networks [4]. Indium Arsenide self-assembled quantum dots (QDs) offer one of the most promising platforms [5] for such applications due to the large tuneability of their emission frequency [6], fast triggered emission rates [7,8], and the possibility of integration into nanostructures [9]. However, charge carriers confined to a semiconductor QD interact with the solid-state environment, in which disparate noise sources cause fluctuations of the central frequency of the optical transitions [10][11][12]. These fluctuations lead to both spectral distinguishability of the fluorescence from independent QDs as well as a decreased emission intensity in resonant excitation and represent a challenge to be overcome in order to achieve a scalable architecture using QDs. Here, we develop an active feedback stabilization scheme which makes use of the phonon-assisted fluorescence intensity as a probe for fluctuations of the zero-phonon line (ZPL) frequency. Our scheme allows for the detection and correction of environment-induced frequency fluctuations in a manner compatible with broadband photon collection strategies. Ideally, the frequency of the QD transition is stabilized without sacrificing any of the photon emission with a high bandwidth and in resonant excitation. Indeed, proposals for efficient linear optical computing with a polarization-entangled photon source require photon collection and detection efficiencies above 0.5 [13,14]. Previously demonstrated frequency stabilization protocols with solid state emitters have a bandwidth limited by periodic measurements of ZPL peak position [15,16], or rely on continuously detecting a fraction of the ZPL [17]. In this letter, we present a technique for simultaneous and discriminatory detection of both the zero-phonon and the phonon-assisted components of the resonance fluorescence (RF) from a single QD. We use the latter to generate an error signal in order to stabilize the intensity of the ZPL emission with a high bandwidth. We sho...

Self-homodyne-enabled generation of indistinguishable photons

“…Moreover, the short lifetime leads to a homogeneous linewidth of the emission which is much larger than that of bulk QDs. Therefore, we expect the indistinguishability to be unaffacted by spectral diffusion of the quantum emitter even without active suppression of the spectral diffusion [36][37][38]. Specifically, in contrast to bulk QDs [8,11] we expect a similarly high indistinguishability for excitation pulses with a longer time delay or for measurements interfering the emission from multiple systems.…”

Suppressing Spectral Diffusion of Emitted Photons with Optical Pulses

“…Due to severity of the problem, solutions have been actively sought, and the schemes based e.g. on active feedback [17][18][19][20], three-level emitters coupled to the cavities [24,25], special emission regimes [26,27], have been explored.Here we suggest a conceptually simple, general, and robust protocol for suppressing the spectral diffusion of the ZPL of the solid-state emitters. Since the frequency of the emitted light is determined by the average phase accumulated between the states of the emitter over the spontaneous emission time, one can modify the emission spectrum by changing the phase between the relevant states with optical pulses.…”

“…Due to severity of the problem, solutions have been actively sought, and the schemes based e.g. on active feedback [17][18][19][20], three-level emitters coupled to the cavities [24,25], special emission regimes [26,27], have been explored.…”

“…At low temperatures, a noticeable fraction of photons emitted from these qubits is concentrated in the zero-phonon line (ZPL) and is insensitive to the phonon absorption/emission. The photons emitted into the ZPL are naturally entangled to the originating solid-state qubits [6,[8][9][10][11][12][13], and constitute excellent flying qubits; the emission into the ZPL can be enhanced by placing the qubit into a cavity [14,15].However, ensuring indistinguishability of the photons emitted by two different quantum dots or color centers remains a crucial challenge [4, 5,[16][17][18][19][21][22][23]. Changes in the local strain and motion of the charges around the emitter lead to slow random variation (spectral diffusion) of the energies of the levels involved in the photon emission.…”

“…However, ensuring indistinguishability of the photons emitted by two different quantum dots or color centers remains a crucial challenge [4, 5,[16][17][18][19][21][22][23]. Changes in the local strain and motion of the charges around the emitter lead to slow random variation (spectral diffusion) of the energies of the levels involved in the photon emission.…”