Liang Zhai

Quantum emitters serve as essential on-demand photonic resources, generating quantum states of light such as single photons and entangled photon pairs while serving as interfaces between light and matter. Buried in the solid state, quantum emitters enable a straightforward adoption of advanced nanofabrication techniques, facilitating precise engineering of their photonic environment for scalable quantum technologies. In this review, we introduce the fundamentals of quantum emitters and the key metrics characterising their performance. We highlight three material platforms: quantum dots, defect centres in diamond, and defect centres in silicon carbide. We summarise the recent developments of these platforms and discuss their advancements in quantum applications, including quantum communication, computation, and sensing. Finally, we provide a comparison across the three platforms, along with an outlook on future directions and potential challenges.

Quantum emitters serve as essential on-demand photonic resources, generating quantum states of light such as single photons and entangled photon pairs while serving as interfaces between light and matter. Buried in the solid state, quantum emitters enable a straightforward adoption of advanced nanofabrication techniques, facilitating precise engineering of their photonic environment for scalable quantum technologies. In this review, we introduce the fundamentals of quantum emitters and the key metrics characterising their performance. We highlight three material platforms: quantum dots, defect centres in diamond, and defect centres in silicon carbide. We summarise the recent developments of these platforms and discuss their advancements in quantum applications, including quantum communication, computation, and sensing. Finally, we provide a comparison across the three platforms, along with an outlook on future directions and potential challenges.

Complete quantum control of a stationary quantum bit embedded in a quantum emitter is crucial for photonic quantum information technologies. Recently, the orbital degree of freedom in optically active quantum dots has emerged as a promising candidate. However, the essential ability to perform arbitrary rotations on orbital qubits remains elusive. Here, we demonstrate arbitrary rotation of a hole orbital qubit with direct phase control using picosecond optical pulses. This is achieved by inducing stimulated Raman transitions within Λ systems coupled via radiative Auger processes. This new capability enables direct control of polar and azimuth angles of the Bloch vector without requiring timed precession. Our results establish orbital states in solid-state quantum emitters as a viable resource for applications in high-speed quantum information processing.

A promising route towards the deterministic creation and annihilation of single-phonons is to couple a single-photon emitter to a mechanical resonator. The challenge lies in reaching the resolved-sideband regime with a large coupling rate and a high mechanical quality factor. We achieve this by coupling self-assembled InAs quantum dots to a small mode-volume phononic-crystal resonator with mechanical frequency Ω_m/2π = 1.466 GHz and quality factor Q_m = 2.1 × 10³. Thanks to the high coupling rate of g_ep/2π = 2.9 MHz, and by exploiting a matching condition between the effective Rabi and mechanical frequencies, we observe the interaction between the two systems via correlations in the emitted photons. Our results represent a major step towards quantum control of the mechanical resonator via a single-photon emitter.

We present experiments in which self-assembled InAs quantum dots are coupled to a thin, suspended-beam GaAs resonator. The quantum dots are driven resonantly and the resonance fluorescence is detected. The narrow quantum dot linewidths, just a factor of 3 larger than the transform limit, result in a high sensitivity to the mechanical motion. We show that one quantum dot couples to eight mechanical modes spanning a frequency range from 30 to 600 MHz: one quantum dot provides an extensive characterization of the mechanical resonator. The coupling spans the unresolved-sideband to the resolved-sideband regimes. Finally, we present the first detection of thermally driven phonon sidebands (at 4.2 K) in the resonance-fluoresence spectrum. Published by the American Physical Society 2024

The optical spectrum of a quantum dot is typically dominated by the fundamental transition between the lowest-energy configurations. However, the radiative Auger process can result in additional redshifted emission lines. The origin of these lines is a combination of Coulomb interaction and symmetry breaking in the quantum dot. In this paper, we present measurements of such radiative Auger lines for a range of InGaAs/GaAs self-assembled quantum dots. We account for the Auger lines with a tight-binding model with a configuration interaction including symmetry breaking via alloy disorder. We show that the model accounts for the intensities of the Auger lines and the changes from quantum dot to quantum dot. We relate our findings to group theory explaining how the reduction in symmetry caused by alloy disorder is essential for the appearance of the radiative Auger lines.