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arXiv:0803.3700 · Applied Physics Letters

Indistinguishable photons from a diode

Anthony J. Bennett, Raj B. Patel, Andrew J. Shields, K. Cooper, P. Atkinson, Christine A. Nicoll, D. A. Ritchie

Published May 12, 2008• 48 citations
arXivHTMLPDF

Abstract

We generate indistinguishable photons from a semiconductor diode containing an InGaAs/GaAs quantum dot. By using an all-electrical technique to populate and control a single-photon emitting state, we filter out dephasing by Stark shifting the emission energy on time scales below the dephasing time of the state. By mixing consecutive photons on a beam splitter, we observe two-photon interference with a visibility of 64%.

DOI
10.1063/1.2918841

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We generate indistinguishable photons from a semiconductor diode containing an InGaAs/GaAs quantum dot. By using an all-electrical technique to populate and control a single-photon emitting state, we filter out dephasing by Stark shifting the emission energy on time scales below the dephasing time of the state. By mixing consecutive photons on a beam splitter, we observe two-photon interference with a visibility of 64%.
Quantum interference lies at the foundation of many protocols for scalable quantum computing and communication with linear optics. To observe these effects the light source must emit photons that are indistinguishable. From a technological standpoint, it would be beneficial to have electrical control over the emission. Here we report of an electrically driven single-photon source emitting indistinguishable photons. The device consists of a layer of InAs quantum dots embedded in the intrinsic region of a p-i-n diode. Indistinguishability of consecutive photons is tested in a two-photon interference experiment under two modes of operation, continuous and pulsed current injection. We also present a complete theory based on the interference of photons with a Lorentzian spectrum which we compare to both our continuous wave and pulsed experiments. In the former case, a visibility was measured limited only by the timing resolution of our detection system. In the case of pulsed injection, we employ a two-pulse voltage sequence which suppresses multi-photon emission and allows us to carry out temporal filtering of photons which have undergone dephasing. The characteristic Hong-Ou-Mandel 'dip' is measured, resulting in a visibility of 64 +/- 4%.
A single-photon source capable of emitting indistinguishable photons is a key element in schemes for scalable quantum information processing with linear optics. Whilst several groups have reported such sources, up until now an electrically driven source capable of making these protocols technologically viable has yet to be reported. We present the first demonstration of an electrically driven single-photon source emitting indistinguishable photons. Our sample consists of a layer of InAs/GaAs quantum dots embedded in the intrinsic region of a p-i-n microcavity diode. We test the indistinguishability of consecutive photons by carrying out a Hong-Ou- Mandel-type two-photon interference experiment whereby two identical photons arriving simultaneously at two input ports of a 50:50 beamsplitter exit together. The device was operated under two modes, continuous and pulsed current injection. In the former case, we measured a coherence time of up to 400 ps at low pump current - the longest reported under these excitation conditions. A two-photon interference visibility was measured, limited only by the timing resolution of our detection system and further suggesting a 100% overlap of photon wavepackets at the output beamsplitter. In the case of pulsed injection, we employed a two-pulse voltage sequence which allowed us to carry out temporal filtering of photons which had undergone dephasing. The characteristic Hong-Ou-Mandel "dip" was measured resulting in a visibility of 64 ± 4%.
We demonstrate interference between discrete photons emitted by two different semiconductor quantum dots and quantify their degree of indistinguishability. The quantum dot emission energies are tuned into resonance by straining the samples. Upon interference on a beamsplitter, the photons are shown to be 18.1% indistinguishable, resulting in a coincidence detection rate below the classical limit. Post-selecting only those detections occurring within a short time of each other increases the measured indistinguishability to 47%. The photons are partially distinguishable due to dephasing of the exciton states, and post-selection is also affected by the detector response time.
Efficient generation and detection of coherent single photons are key to advances in photonic quantum technologies such as quantum computation, quantum simulation, and quantum communication. Among many quantum emitters, semiconductor quantum dots are promising due to their deterministic and high-rate single-photon emission and the possibility of integration into nanostructures. However, poor quantum coherence between single photons created by independent emitters poses a major roadblock. Here, we present near-unity two-photon interference visibilities from two separate GaAs quantum dots. This high visibility (~93%) is achieved under rigorous conditions: there is no Purcell enhancement, no temporal post-selection, no narrow spectral filtering, nor frequency stabilization. One key component is the heterostructure, an n-i-p diode using material of excellent quality. The quantum dot charge is locked via Coulomb blockade; within a charging plateau, the exact emission frequency can be tuned via the bias applied to the gate; the charge noise is very low. A second key component is the quantum dot itself: the relatively large size confers multiple benefits. Our results suggest that GaAs quantum dots represent a versatile choice for generating identical photons from multiple emitters.
The authors present steps toward the experimental realization of indistinguishable single photon sources based on independent unstrained GaAs quantum dots (QDs), which are embedded in planar cavities to improve the light collection efficiency. The emission lines of two QDs are brought into resonance and overlapped at a beam splitter. The coherence properties of the emitted photons are investigated by measuring the first-order field correlation function. Despite the fact that the short dephasing time of the selected QDs prevents us to observe quantum interference between the two photons, the approach could be applied to other QDs.
The generation of indistinguishable single photons is a fundamental requirement for photonic quantum technologies. However, spectral fluctuations, often induced by charge noise in epitaxial quantum dots (QDs), lead to exciton dephasing, thereby limiting their practical usage in quantum applications. We present a straightforward approach to mitigate charge noise-induced decoherence in droplet-etched GaAs QDs embedded in an n-i-p diode structure and integrated deterministically into an electrically contacted circular Bragg grating resonator for emission enhancement. The quantum device allows for the stabilization of the charge environment by applying an external electrical field while producing a photon extraction efficiency of (37±2)%. Hong-Ou-Mandel two-photon interference measurements reveal a strong dependence of the exciton dephasing time and interference visibility on the applied bias, in excellent agreement with our theoretical predictions. Notably, the reduction in visibility from a maximum, charge stabilized corrected value of 97% at the optimum bias point follows an inverse square dependence (∝1/I^{2}) with increasing diode current (I) in the forward direction. Under a quasi-resonant excitation scheme, we achieve a maximum exciton dephasing time (T_{2}^{*}) of approximately (6.8±0.5) ns, reaching nearly the Fourier limit (T_{2}=2T_{1}) without the need for complex echo schemes like Ramsey or Carr-Purcell-Meiboom-Gill sequences. These findings are consistent with theoretical predictions from rate equation modeling and quantum optical analysis, as well as voltage-dependent linewidth measurements, demonstrating optimized electrical control of exciton dephasing.