A Quantum Computer in a Diamond Grant Riley

Outline Requirements for a quantum computer Chemical Vapor Deposition Diamonds – Properties – Impurities (the good kind) Nitrogen vacancy spin center Multi-qubit register

Quantum computing Entangled bits (qubits) – Different kinds of bits available Photon polarization Nuclear spin Electron spin – Readout and storage are challenging Superposition states – Advantage over classical computers

CVD Diamonds Grown in large reactors Low pressure – 0.145–3.926 psi – 1 atm = 14 psi Energy source – Hot filament – Arc discharges Substrate – 16 inch diameter (largest) – 4mm x 4mm (this application) Polycrystalline or Single Crystal

Diamond Applications Radiation sensors – Wide band-gap – Metallization friendly Heat Sinks – Highest thermal conductivity of any solid material Damage proof coatings and small mechanical parts

Impurities Many impurities can be introduced during the growth process – Nitrogen Vacancy 2 unbound electrons from nitrogen 3 electrons from vacancy side carbon exchange with the unbound nitrogen electrons 1 additional electron located at the vacancy site Forms a spin=1 pair with a vacancy electron N V

Nitrogen vacancy The Nitrogen atom also has a nuclear spin of 1 The spins couple to form a ground state spin triplet Can be read out without destroying quantum state Electron transitions

Nitrogen Spin Manipulation

Multiple Controlled gate

Summary and Scaling up In this paper 3 controlled NOT gate was achieved – Single shot readout is very fast – Can be scaled up Temperature dependent (paper results taken at 8.6 K) – High temp means more spin mixing – De-excitation times much faster Opportunities for exploring 2 particle quantum correlations Diamond growing is prone to problems – Companies use proprietary methods – Come and go frequently