1. 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

2. 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

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

4. 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. . .

5. Introduction Our research
Pulsed ESR at 4, 8 and 12 T
GWM, L-C Brunel and J van Tol, Rev Sci Instrum 79, (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, (2007)
CW ESR: J van Tol, L C Brunel and R J Wylde, Rev Sci Inst 76, (2005)

6. 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

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

8. 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

9. 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 (1973)
A Honig & M Moroz, RSI (1978)
GWM, DR McCamey, HA Seipel, LC Brunel,
J van Tol & C. Boehme, PRL 101, ,
(2008) e
B0 = 8.6 T
T = 2.8 K
Then go to pulsed mode
10 micron
Sensitivity: need (100 nm)3 sample

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

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

12. 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, (2008),
PRL 102, (2009),
PRB 78, (2008)
DR McCamey, J van Tol, GWM & C. Boehme, PRL 102, (2009)

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

14. 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, (2008)

15. 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, (2008)

16. 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, (2008)

17. 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, (2008)

18. 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, (2008)

19. 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, (2008)

20. 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, (2008)

21. 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, (2008)

22. 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 (2004)
A M Stoneham, A H Harker & GWM, in press at J Phys CM, arXiv:
Qubit 1
Control
Qubit 2
Three theory papers
light

23. 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

24. 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