Quantum dot single-photon source

A laser pulse can excite a pair of carriers known as an exciton in the quantum dot.

The emission of single photons can be proven by measuring the second order intensity correlation function.

The spontaneous emission rate of the emitted photons can be enhanced by integrating the quantum dot in an optical cavity.

Additionally, the cavity leads to emission in a well-defined optical mode increasing the efficiency of the photon source.

A single-photon source based on a quantum dot in a microdisk structure was reported in 2000.

[2] Sources were subsequently embedded in different structures such as photonic crystals[3] or micropillars.

[5] Most quantum dot single-photon sources need to work at cryogenic temperatures, which is still a technical challenge.

[5] The other challenge is to realize high-quality quantum dot single-photon sources at telecom wavelength for fiber telecommunication application.

[6] The first report on Purcell-enhanced single-photon emission of a telecom-wavelength quantum dot in a two-dimensional photonic crystal cavity with a quality factor of 2,000 shows the enhancements of the emission rate and the intensity by five and six folds, respectively.

In this model, the quantum dot only interacts with one single mode of the optical cavity.

To eliminate the probability of the simultaneous emission of two photons it has to be made sure that there can only be one exciton in the cavity at one time.

The discrete energy states in a quantum dot allow only one excitation.

If the energy of the pump laser is tuned on resonance, the second exciton cannot be created.

[5] For optical pumping, a pulsed laser can be used for excitation of the quantum dots.

In order to have the highest probability of creating an exciton, the pump laser is tuned on resonance.

There are several ways to realize a quantum dot-cavity system that can act as a single-photon source.

A list of different experimental realizations is shown below: Single photon sources exhibit antibunching.

To verify the antibunching of a light source, one can measure the autocorrelation function

The theoretical solution of the Jaynes-Cummings Hamiltonian is a well-defined mode in which only the polarization is random.

Two photons of the source are prepared so that they enter a 50:50 beam splitter at the same time from the two different input channels.

[13][10] Single-photon sources are of great importance in quantum communication science.

[5] Single photons entering a beam splitter exhibit inherent quantum indeterminacy.

Random numbers are used extensively in simulations using the Monte Carlo method.

It works with a light source that perfectly emits only one photon at a time.

Apart from that, single photon sources can be used to test some fundamental properties of quantum field theory.

Figure 1: Schematic structure of an optical microcavity with a single quantum dot placed between two layers of DBR's. This structure works as a single photon source.
Figure 2: The decay of a linewidth broadened excited state results in the emission of a photon of frequency ħω. The linewidth broadening is a result of the finite lifetime of the excited state.