Single-shot detection of electrons generated by individual photons in a tunable lateral quantum dot

Angular momentum transfer from photon polarization to an electron spin in a gate-defined quantum dot

Gate-defined quantum dots (QDs) are such a highly-tunable quantum system in which single spins can be electrically coupled, manipulated, and measured. However, the spins in gate-defined QDs are lacking its interface to free-space photons. Here, we verify that a circularly-polarized single photon can excite a single electron spin via the transfer of angular momentum, measured using Pauli spin blockade (PSB) in a double QD. We monitor the inter-dot charge tunneling which only occur when the photo-electron spin in one QD is anti-parallel to the electron spin in the other. This allows us to detect single photo-electrons in the spin-up/down basis using PSB. The photon polarization dependence of the excited spin state was finally confirmed for the heavy-hole exciton excitation. The angular momentum transfer observed here is a fundamental step providing a route to instant injection of spins, distributing single spin information, and possibly towards extending quantum communication.

Gate-defined quantum dots offer a way to engineer electrically controllable quantum systems with potential for information processing. Here, the authors transfer angular momentum from the polarization of a single photon to the spin of a single electron in a gate-defined double quantum dot.

Single-electron charge sensing in self-assembled quantum dots

Measuring single-electron charge is one of the most fundamental quantum technologies. Charge sensing, which is an ingredient for the measurement of single spins or single photons, has been already developed for semiconductor gate-defined quantum dots, leading to intensive studies on the physics and the applications of single-electron charge, single-electron spin and photon–electron quantum interface. However, the technology has not yet been realized for self-assembled quantum dots despite their fascinating transport phenomena and outstanding optical functionalities. In this paper, we report charge sensing experiments in self-assembled quantum dots. We choose two adjacent dots, and fabricate source and drain electrodes on each dot, in which either dot works as a charge sensor for the other target dot. The sensor dot current significantly changes when the number of electrons in the target dot changes by one, demonstrating single-electron charge sensing. We have also demonstrated real-time detection of single-electron tunnelling events. This charge sensing technique will be an important step towards combining efficient electrical readout of single-electron with intriguing quantum transport physics or advanced optical and photonic technologies developed for self-assembled quantum dots.

Single electron-photon pair creation from a single polarization-entangled photon pair

Quantum entanglement between different forms of qubits is an indication of the universality of quantum mechanics. Entanglement transfer between light and matter, especially photon and spin, has long been studied as the central concept, but it remains technically challenging for single photons and spins. In this paper, we show paired generation of a single electron in a GaAs quantum dot and a single photon from a single polarization-entangled photon pair. We measure temporal coincidence between the single photo-electron detection and the single photon detection. Considering a single photon polarization is converted to an electron spin via an optical selection rule, the present result indicates the capability of photon to spin entanglement transfer. This may be useful to explore the physics of entanglement transfer and also for applications to quantum teleportation based quantum communication.

Nondestructive real-time measurement of charge and spin dynamics of photoelectrons in a double quantum dot

We demonstrate one and two photoelectron trapping and the subsequent dynamics associated with interdot transfer in double quantum dots over a time scale much shorter than the typical spin lifetime. Identification of photoelectron trapping is achieved via resonant interdot tunneling of the photoelectrons in the excited states. The interdot transfer enables detection of single photoelectrons in a nondestructive manner. When two photoelectrons are trapped at almost the same time we observed that the interdot resonant tunneling is strongly affected by the Coulomb interaction between the electrons. Finally the influence of the two-electron singlet-triplet state hybridization has been detected using the interdot tunneling of a photoelectron.