Semiconductor quantum light sources

Abstract

Lasers and LEDs display a statistical distribution in the number of photons emitted in a given time interval. New applications exploiting the quantum properties of light require sources for which either individual photons, or pairs, are generated in a regulated stream. Here we review recent research on single-photon sources based on the emission of a single semiconductor quantum dot. In just a few years remarkable progress has been made in generating indistinguishable single-photons and entangled photon pairs using such structures. It suggests it may be possible to realise compact, robust, LED-like semiconductor devices for quantum light generation. Applications of Quantum PhotonicsApplying quantum light states to photonic applications allows functionalities that are not possible using 'ordinary' classical light. For example, carrying information with single-photons provides a means to test the secrecy of optical communications, which could soon be applied to the problem of sharing digital cryptographic keys.1 2 Although secure quantum key distribution systems based on weak laser pulses have already been realised for simple point-to-point links, true single-photon sources would improve their performance.3 Furthermore, quantum light sources are important for future quantum communication protocols such as quantum teleportation. 4Here quantum networks sharing entanglement could be used to distribute keys over longer distance or through more complex topologies. 5A natural progression would be to use photons for quantum information processing, as well as communication. In this regard it is relatively straightforward to encode and manipulate quantum information on a photon. On the other hand, single-photons do not interact strongly with one-another, a prerequisite for a simple photon logic gate. In linear optics quantum computing 67 (LOQC) this problem is solved using projective measurements to induce an effective interaction between the photons. Here triggered sources of single-photons and entangled pairs are required as both the qubit carriers, as well as auxiliary sources to test the successful operation of the gates. Although the component requirements for LOQC are challenging, they have recently been relaxed significantly by new theoretical schemes.7 Quantum light states are also likely to become increasingly important for various types of precision optical measurement. 8For these applications we would ideally like light sources which generate pure single-photon states "on demand" in response to an external trigger signal. Key performance measures for such a source are the efficiency, defined as the fraction of photons collected into the experiment or application per trigger, and the second order correlation function at zero delay, see text box. The latter is essentially a measure of the two-photon rate compared to a classical source with random emission times of the same average intensity. In order to construct applications involving more than one photon, it is also important that photons emitted from th...

Directed self‐assembly of single quantum dots for telecommunication wavelength optical devices

“…Sources that can generate pure single-photon states on demand [8,9] form the basis of future technologies in the field of quantum information pro-cessing. Owing to their atomic-like energy spectrum, quantum dots can be regarded as a two-level quantum system [1] that can generate exactly one single photon, or entangled photon pair, per excitation trigger pulse.…”

Enhanced indistinguishability of in-plane single photons by resonance fluorescence on an integrated quantum dot

“…The critical parameters are the measured emission lifetime and coherence time T 1 = 0.70 ns and T 2 = 1.47 ns, respectively, as well as the Rabi parameter that is related to the Rabi frequency. Under resonant excitation conditions, the second-order correlation function g (2) (t) is given by:…”

“…The bunching effect has been included using an exponential decay with characteristic time constant T b = 8 ns.. At low excitation condition (with Rabi parameter = 0.01, which corresponds to 0.01 · (2 ) -1 Rabi cycles/ns), the model fails to reproduce the experimental g (2) (t) (Fig. 3(b), blue dashed line), in particular the strong bunching observed at short positive and negative time delays (at t = ± 1.5 ns).…”

“…29 (raw data 0.18 ± 0.01). The degree of the in-plane photon indistinguishability is defined by the TPI visibility, which is given by V (t) = (g orth (2) (t) -g par (2) (t)) / g orth (2) (t). This post-selective measurement is valid since the temporal resolution of our set up is much shorter than the photon coherence time.…”

“…2 Using optical excitation or electrical carrier injection, single QDs have proven to be excellent single-photon [3][4][5] and entangled photon-pair emitters. 6,7 At the heart of the proposed protocols for two-qubit gates in linear optics quantum computation lies the interference of single-photon pulses on a beam splitter.…”