A Quantum Computer in a Diamond Grant Riley. Outline Requirements for a quantum computer Chemical...
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Transcript of A Quantum Computer in a Diamond Grant Riley. Outline Requirements for a quantum computer Chemical...
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