The remarkable coherence and control characteristics of donor spin qubits in silicon, with their intrinsic CMOS compatibility, make them ideal qubits for QI applications, even when compared with NV centers in diamond and quantum dots. However, a robust and scalable QI system is yet to be demonstrated on these qubits. Compared to the group V hydrogenic donors such as phosphorus, the deep chalcogen donors (sulfur, selenium and tellurium) offer significantly larger electron binding energy, especially when singly ionized, which makes them suitable for optical control through cavity quantum electrodynamics. Particularly, by implanting 77Se+ ions into silicon photonic crystal cavities with high quality factors (Q) and small mode volumes would enable coupling and readout of qubits with a spin-photon interface in midIR wavelength range under the strong-coupling regime.

With a goal to realize a silicon photonics QI platform with donor spin qubits, this project involves a few inherently connected directions. All these directions will more or less involve: theoretical study of condensed matter, quantum/nonlinear optical, or QI systems; numerical simulation and design with commercial software such as Lumerical FDTD and COMSOL; experimental study of photonic systems and light-matter interaction; and fun.

  1. Photonic crystal cavity. Design photonic crystal cavities with high Q (>105) and small mode volumes (<(l/n)3) that resonate at ~2.9mm optical wavelength, which is the 1s:AÛ1s:G7 optical transition for the 77Se+ ion in isotopically purified silicon. With the atomic transition linewidth being at MHz scale, a fine-tuning mechanism should also be designed to match the resonant wavelength with the atomic transition to enable strong-coupling and spin readout.
  2. Deterministic entangled midIR single photon source. Deterministic single photons are required for the control of deep donor qubits to realize QI systems. Possible schemes are electrically-pumped deep donor system, pair sources from nonlinear conversions in new materials, and nonlinear down-conversion of existing single photon sources.
  3. MidIR superconducting single photon detector (SSPD). A single photon detection system with near unity quantum efficiency, low dark count and bandwidth is essential to realize QI systems. SSPD based on photonic crystal coherent absorbers have shown great strength in detecting single photons in communication wavelength but remains challenging for midIR. New geometries and materials are to be proposed and studied.
  4. Integrated QI circuit. Design scalable QI circuits with deep donor qubits aiming at realizing on-chip quantum computation. Also involves design of integrated silicon photonic elements operate at midIR and demonstration of basic quantum operations.
  5. Free to propose other projects…
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