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

• Prepare electronic spin into -1 or +1 spin state• Apply a 180 degree (pi) pulse at 2.874 GHz– This rotates the electron spin to S=0 only if nuclear spin is -1

• Read out spin (watch for de-excitation photons)We’ve prepared

This corresponds to a CNOT Operation, controlled by the Nuclear spin

Multiple Controlled gate

• Can make a similar measurement using a nitrogen spin coupled with nearby carbons

• CCCNOT gate using the lowest total spin state

Electronic spin has minimalpushback on nuclear spins somultiple measurements canbe performed withoutdestroying the state

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