Long-lived spin coherence in silicon with electrical readout Gavin W Morley London Centre for Nanotechnology and Department of Physics and Astronomy, UCL Funding: Quantum Coherent Properties of Spins II, PITP, 6th December 2009

People Involved in this Work Introduction People Involved in this Work University of Utah Christoph Boehme Dane R McCamey Heather A Seipel National High Magnetic Field Laboratory Hans van Tol Louis-Claude Brunel

Phosphorus dopants in silicon Introduction Phosphorus dopants in silicon - Long spin coherence (A M Tyryshkin et al, PRB 68, 193207 2003) - Atomic positioning (S R Schofield et al, PRL 91, 136104 2003) - Control wavefunction size (N Q Vinh et al, PNAS 105, 10649 2008) Previous work

Towards quantum computing Introduction Introduction Our research Towards quantum computing Experimental challenges: Initialization Control superposition and entanglement Decoherence Readout we have a plan Turn this around: use a quantum system to keep track of everything and measure it to see the result. However, this is experimentally hard. If you can do everything on this list at the same time then you can do a quantum computation. You would not choose the kind of biomolecule I just showed. Theory shows QC can solve some problems better than a classical PC, but no-one has built a QC. For my experiments, Initialization means a large spin polarization. We control superposition and entanglement with magnetic resonance, faster than the decoherence in the system. At the end we need a readout, and this leads me to use an electrical readout. Magnetic resonance is central to all of these things. . .

Introduction Our research Pulsed ESR at 4, 8 and 12 T GWM, L-C Brunel and J van Tol, Rev Sci Instrum 79, 064703 (2008) ESR is MR of electrons. Need high fields where P>95%. Normal ESR is 0.3 T where P<10% At NHMFL we built a pulsed ESR spectrometers that operates at 12.5 T: the highest in the world Nuclear Spin Polarization: GWM, J van Tol, A Ardavan, K Porfyrakis, J Zhang and G A D Briggs, Phys Rev Lett 98, 220501 (2007) CW ESR: J van Tol, L C Brunel and R J Wylde, Rev Sci Inst 76, 074101 (2005)

Introduction Our research Visible light creates electron-hole pairs Circularly polarized 240 GHz radiation manipulates electron spins DC current source reacts slowly 1 mm overlap Fast current detector measures signal A silicon 10 micron B0 = 8.6 T T = 2.8 K Measure current instead of reflected MW

Continuous-wave electrically-detected magnetic resonance Introduction Our research Continuous-wave electrically-detected magnetic resonance Our papers: PRL 101, 207602 (2008), PRL 102, 027601 (2009), PRB 78, 045303 (2008) Fingerprint match for Si:P. note y axis. Nuclear spin readout. Why is there a signal at all?

Introduction Our research Visible light creates electron-hole pairs Circularly polarized 240 GHz radiation manipulates electron spins DC current source reacts slowly 1 mm overlap Fast current detector measures signal A silicon B0 = 8.6 T T = 2.8 K Microscopic model shows spin dependent conductivity 10 micron

Sensitivity: need (100 nm)3 sample Introduction Our research Visible light creates electron-hole pairs Circularly polarized 240 GHz radiation manipulates electron spins h h e e DD Thornton & A Honig, PRL 30 909 (1973) A Honig & M Moroz, RSI 49 183 (1978) GWM, DR McCamey, HA Seipel, LC Brunel, J van Tol & C. Boehme, PRL 101, 207602, (2008) e B0 = 8.6 T T = 2.8 K Then go to pulsed mode 10 micron Sensitivity: need (100 nm)3 sample

Continuous-wave electrically-detected magnetic resonance Introduction Our research Continuous-wave electrically-detected magnetic resonance Our papers: PRL 101, 207602 (2008), PRL 102, 027601 (2009), PRB 78, 045303 (2008) Note small difference in line strengths… DNP

Continuous-wave electrically-detected magnetic resonance Introduction Our research Continuous-wave electrically-detected magnetic resonance Our papers: PRL 101, 207602 (2008), PRL 102, 027601 (2009), PRB 78, 045303 (2008) Nuclear T1 DR McCamey, J van Tol, GWM & C. Boehme, PRL 102, 027601 (2009)

Continuous-wave electrically-detected magnetic resonance Introduction Our research Continuous-wave electrically-detected magnetic resonance P < 0 P = 0 Thermal Equilibrium Flip-flop, GX Capture-emission, GCE Thermal Equilibrium Thermal Equilibrium Flip-flop, GX Nuclear T1 Our papers: PRL 101, 207602 (2008), PRL 102, 027601 (2009), PRB 78, 045303 (2008) DR McCamey, J van Tol, GWM & C. Boehme, PRL 102, 027601 (2009)

Continuous-wave electrically-detected magnetic resonance Introduction Our research Continuous-wave electrically-detected magnetic resonance Our papers: PRL 101, 207602 (2008), PRL 102, 027601 (2009), PRB 78, 045303 (2008) Fingerprint match for Si:P. note y axis. Nuclear spin readout. Why is there a signal at all?

Transient response to a 240 GHz pulse Introduction Our research Transient response to a 240 GHz pulse Spin dynamics. Use a pi pulse which is 180degrees GWM, DR McCamey, HA Seipel, LC Brunel, J van Tol & C. Boehme, PRL 101, 207602 (2008)

Rabi Oscillations Introduction Our research Isidor Isaac Rabi (1898 – 1988) Control superposition all the way around and back to where you started GWM, DR McCamey, HA Seipel, LC Brunel, J van Tol & C. Boehme, PRL 101, 207602 (2008)

Rabi Oscillations Introduction Our research Reduce MW power and oscillations go slower. Rabi decay is few microseconds GWM, DR McCamey, HA Seipel, LC Brunel, J van Tol & C. Boehme, PRL 101, 207602 (2008)

Spin echo Introduction Our research Erwin L Hahn (born 1921) Spin echo animation by Chris Noble True spin coherence- time that superposition survives GWM, DR McCamey, HA Seipel, LC Brunel, J van Tol & C. Boehme, PRL 101, 207602 (2008)

Electrically-detected spin echo Introduction Our research Electrically-detected spin echo Nuclear T1 GWM, DR McCamey, HA Seipel, LC Brunel, J van Tol & C. Boehme, PRL 101, 207602 (2008)

Decay of electrically-detected spin echoes Introduction Our research Decay of electrically-detected spin echoes Nuclear T1 GWM, DR McCamey, HA Seipel, LC Brunel, J van Tol & C. Boehme, PRL 101, 207602 (2008)

Decay of electrically-detected spin echoes Introduction Our research Decay of electrically-detected spin echoes Nuclear T1 GWM, DR McCamey, HA Seipel, LC Brunel, J van Tol & C. Boehme, PRL 101, 207602 (2008)

Decay of electrically-detected spin echoes Introduction Our research Decay of electrically-detected spin echoes Nuclear T1 GWM, DR McCamey, HA Seipel, LC Brunel, J van Tol & C. Boehme, PRL 101, 207602 (2008)

Entangling multiple qubits: theory Introduction Our research Entangling multiple qubits: theory A M Stoneham, A J Fisher & P T Greenland, J Phys CM 15 L477 (2003) R Rodriquez, A J Fisher, P T Greenland & A M Stoneham, J Phys CM 16 2757 (2004) A M Stoneham, A H Harker & GWM, in press at J Phys CM, arXiv:0904.4895 Qubit 1 Control Qubit 2 Three theory papers light

Entangling multiple qubits Introduction Our research Entangling multiple qubits Bismuth is a good as phosphorus The other species? bismuth in silicon has even better spin coherence than Si:P

Conclusions Experimental challenges: Initialization Introduction Our research Conclusions and future work Conclusions Experimental challenges: Initialization Control superposition and entanglement Decoherence Readout we have a plan 25 times Higher field than previous pEDMR gives polarization+ higher sensitivity without destroying long coherence times. We have demonstrated superpositions. We have a plan for readout in silicon