QLUSTER research groups led by Hagai Eisenberg and Pascale Senellart have achieved the generation of a 4-photon cluster state! Single photons were generated in a highly efficient quantum dot - cavity device and subsequently entangled in a compact fiber-loop setup. The entanglement is encoded in the polarization degree of freedom, and all photons are in a common spatial mode. The reported architecture can be programmed for linear-cluster states of any number of photons, that are required for photonic one-way quantum computing schemes.
Most cavity-based single photon sources operate in the weak coupling regime of cavity QED, and due to material birefringence and fabrication imperfections the optical cavity modes are usually polarization-split. In this paper physicists from Leiden have developed a simple analytic semi-classical model that allows accurate prediction of the response from polarized quantum dot (or atom) transitions in a birefringent cavity, and demonstrate improvement of a single photon source based on it.
Physicists at C2N have demonstrated for the first time the direct generation of light in a state that is simultaneously a single photon, two photons, and no photon at all. They showed that the same kind of light emitter used for decades is also able to generate these quantum states, and expect that this holds true for any kind of atomic system.
The strong-coupling regime of cavity quantum electrodynamics (QED) represents the light–matter interaction at the fully quantum level, for instance, a single photon shifts the resonance frequencies significantly. However, miniaturizing semiconductor cavities without introducing charge noise and scattering losses remained a challenge. Here we present a gated, ultralow-loss, frequency-tunable quantum-dot microcavity device in the strong coupling limit overcoming all of the mentioned shortcomings.
Semiconductor quantum dots offer the highest rate and quality of single photons among all other solid-state quantum light sources. However, they lack access to a long-lived quantum memory, such as a proximal nuclear spin, that would make them competitive for large-scale quantum architectures. Gangloff et al. used the spin of a single electron and light to cool an ensemble of about 30,000 nuclei within semiconductor quantum dots. They then extended this approach to manipulate individual nuclear spins. The ability to manipulate the ensemble of nuclei coherently, down to the single nuclear spin, could lead to the realization of a quantum dot network where each node has its own dedicated quantum memory.