1 / 49

Single-shot read-out of one electron spin

Single-shot read-out of one electron spin. QIP Workshop Newton Institute, Cambridge 27-30 Sep. 2004. Lieven Vandersypen Jeroen Elzerman Ronald Hanson Laurens Willems van Beveren Frank Koppens Ivo Vink Wouter Naber Leo Kouwenhoven. 2. 1. F. F. 6. 3. F. 12 C. 13 C. 7. 13 C. F.

deanna-hancock
Télécharger la présentation

Single-shot read-out of one electron spin

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Single-shot read-out of one electron spin QIP Workshop Newton Institute, Cambridge 27-30 Sep. 2004 Lieven Vandersypen Jeroen Elzerman Ronald Hanson Laurens Willems van Beveren Frank Koppens Ivo Vink Wouter Naber Leo Kouwenhoven

  2. 2 1 F F 6 3 F 12C 13C 7 13C F 12C 5 4 Fe F CO C5H5 CO A seven-spin NMR quantum computer Vandersypen et al., Nature414, 883 (2001) Vandersypen & Chuang, RMP, Oct 2004. 15 = 3 x 5

  3. SL SR Quantum computing with electron spins Loss & DiVincenzo, PRA 1998Vandersypen et al., Proc. MQC02 (quant-ph/0207059) Initialization1 electron, low T, high B0 H0 ~ Swi szi Read-out convert spin to charge then measure charge Read-out convert spin to charge then measure charge ESRpulsed microwave magnetic field HRF ~ S Ai(t) cos(wi t) sxi SWAPexchange interaction HJ ~ S Jij (t) si ·sj Coherencemeasure coherence time in 2DEG:T2 > 100 ns (Kikkawa&Awschalom, 1998)

  4. Electrical single-shot spin measurement Convert spin to charge, then measure charge Loss & DiVincenzo, PRA 1998

  5. Outline (1) one-electron quantum dots… (3) …fast charge detection… (4) ….single spin measurement! (2) …two-level system…  EZ = gmBB 

  6. Outline: we need… (1) one-electron double dots… (3) …fast charge detection… (4) ….single spin measurement! (2) …two-level system…  EZ = gmBB 

  7. A quantum dot as a one-electron box • Electrically measured (contact to 2DEG) • Electrically controlled (gated tunnel barriers, dot potential)

  8. A quantum point contact (QPC) as a charge detector Field et al, PRL 1993

  9. 01 00 12 11 10 (V) (V) 22 21 L L V V -1.02 (V) (V) V V PR PR -0.96 -0.15 -0.30 Few-electron double dotTransport through QPC J.M. Elzerman et al., PRB 67, R161308 (2003) dIQPC/dVL 0 Tesla -1.1 00 -0.9 0 -0.6 • Double dot can be emptied • QPC can detect all charge transitions

  10. Outline: we need… (1) one-electron double dots… (3) …fast charge detection… (4) ….single spin measurement! (2) …two-level system…  EZ = gmBB 

  11. T DRAIN SOURCE Q G 200 nm M R P Energy level spectroscopy at B = 0 10 dIDOT/dVSD VSD(mV) 0 N=1 N=0 Ground and excited state Ground state Notransport B = 0T -10 -653 -695 VT(mV) • E ~ 1.1meV • EC ~ 2.5meV

  12. 2 B=0 B> 0 ES  VSD (mV) N=0 0 gmBB GS  0T -2 2 |g|=0.44 0.2 VSD (mV) DEZ (meV) N=1 N=1 N=0 N=0 0 0.1 6T 10T -2 0 VT(mV) VR (mV) -657 -675 -995 -1010 15 0 5 10 B// (T) Single electron Zeeman splitting in B// Hanson et al, PRL 91, 196802 (2003)Also: Potok et al, PRL 91, 016802 (2003)

  13. T Q M R P Excited-state spectroscopy on a nearly-closed quantum dot Elzerman et al, APL 84, 4617, 2004Also: Johnson, cond-mat/04 DRAIN 0 t t IQPC -VP time RESERVOIR DIQPC time 200 nm G SOURCE EF G • Apply pulse train to gate P • Measure amplitude of pulse-response with lock-in amplifier Electron tunneling  small pulse response

  14. Zeeman splitting for N = 1 10 DEZ lock-in signal (arb.units) VP (mV) B = 10 T N = 0 N = 1 -1.150 -1.135 VM (V) f = 385 Hz 1 -1.13 VM (V) -1.15 Geff G

  15. T0 T- T+ T0 VSD (mV) S S N=2 N=1 Gate voltage Expt: Hanson et al, cond-mat/0311414, Theory: Recher et al, PRL 85,1962, 2000 Bipolar spin filter 0 VSD (mV) 0 N=1 N=0 Gate voltage

  16. Outline: we need… (1) one-electron double dots… (3) …fast charge detection… (4) ….single spin measurement! (2) …two-level system…  EZ = gmBB 

  17. T Q M R P Fast charge detection DRAIN • VA = 0.8nV/Hz1/2 (white) • IA = 0.4 pA/Hz1/2 @ 40 kHz (~ f ) • CL = 1.5 nF • Operating BW: 40 kHz • Shot-noise limit: 40 MHz RESERVOIR IQPC G 200 nm SOURCE

  18. T Q M R P Observation of individual tunnel events Vandersypen et al, APL, to appear (see cond-mat/0407121) DRAIN RESERVOIR IQPC G 200 nm SOURCE • VSD = 1 mV • IQPC ~ 30 nA • ∆IQPC ~ 0.3 nA • Shortest steps ~ 8 µs

  19. Pulse-induced tunneling response to electron tunneling 0.8 response to pulse 0.4 DIQPC (nA) 0.0 -0.4 0 0.5 1.0 1.5 Time(ms)

  20. Outline: we need… (1) one-electron double dots… (3) …fast charge detection… (4) ….single spin measurement! (2) …two-level system…  EZ = gmBB 

  21. Spin read-out principle:convert spin to charge charge SPIN UP 0 -e time N = 1 charge SPIN DOWN 0 -e time N = 1 N = 0 N = 1 ~G-1

  22. Spin read-out procedure inject & wait read-out spin empty QD empty QD Vpulse DIQPC Inspiration: Fujisawa et al., Nature 419, 279, 2002

  23. Spin read-out results Elzerman et al., Nature 430, 431, 2004 inject & wait read-out spin empty QD empty QD Vpulse DIQPC 2 “SPIN UP” “SPIN DOWN” DIQPC (nA) 1 0 0 0 0.5 1.0 0.5 1.0 1.5 1.5 Time (ms) Time (ms)

  24. Verification spin read-out Spin down fraction Waiting time (ms)

  25. Measurement of T1 B = 8 T T1 ~ 0.85 ms B = 10 T T1 ~ 0.55 ms • Surprisingly long T1 • T1goes up at low B B = 14 T T1 ~ 0.12 ms Elzerman et al., Nature 430, 431, 2004

  26. Single-shot read-out fidelity 1.0 spin: outcome: 0.8 0.93 “up”  0.6 a=0.07 a 1-b 65% 0.4 b=0.28 0.2 “down”  0.0 0.72 0.6 0.8 1.0 visibility = 1-a-b  0.65 Threshold (nA) • a = Pr[ escapes] • b = Pr[miss step] + Pr[relaxes] • Future improvements: • a: lower Tel • b: faster charge detection

  27. SL SR Outlook Initialization1 electron, low T, high B0 H0 ~ Swi szi Read-out convert spin to charge then measure charge ESRpulsed microwave magnetic field HRF ~ S Ai(t) cos(wi t) sxi SWAPexchange interaction HJ ~ S Jij (t) si ·sj Coherencemeasure coherence time T1 is long; T2 = ??

  28. z B0 fLarmor S 250 nm fres B1 B1 y B0 S’ IAC Single Electron Spin Resonance W W 250 μm x B1 = 1 mT fRabi~ 5 MHz

  29. ESR induced current peak GL GR mS ISD mD Detection of Continuous Wave ESR Engel & Loss, PRL 86, 4648 (`01) GL, GR =10 MHz T2 =100 ns For 1.1 mT (~ -10dBm) Peak is only 300 fA 300 fA

  30. 0.8 I (pA) 0.0 -1.023 Electric field dominates signal! Photon Assisted TunnelingPumping -1.029 gate voltage (V) Electron transport under CW microwaves from -60dBm to -40dBm hf hf

  31. Pulsed ESR scheme Apply microwaves Read out spin state electric field component no longer hinders ESR detection

  32. ESR in a Si-FET channel M. Xiao et al.Nature 430, 435 (‘04)

  33. 00 Summary http://qt.tn.tudelft.nl/research/spinqubits Spin qubit ideas Vandersypen et al, Proc. MQC02,quant-ph/0207059 Engel et al. PRL (to appear) Tunable few-electron double dot Elzerman et al., PRB 67, R161308, 2003 DC or LOCK-IN SINGLE-SHOT Zeeman splitting Fast charge detection Hanson et al, PRL 91, 196802, 2003 Vandersypen et al, APL to appear, cond-mat/0407121 Bipolar spin filter Single-shot spin read-outT1 ~ 0.85 ms (8 T) Hanson et al, cond-mat/0311414 Excited states using QPC Elzerman et al, Nature 430, 431, 2004 Elzerman et al, APL 84, 4617, 2004

  34. Ciorga ’99 QPC-R QPC-L Open design GaAs/AlGaAs heterostructure 2DEG 90 nm deep ns = 2.9 x 1011 cm-2 Tunable double dot design T IDOT IQPC IQPC Field ’93Sprinzak ’01 PR PL R L M QPC for charge detection

  35. 01 00 12 -1.02 11 10 (V) 22 21 L V -0.96 (V) V -0.15 -0.30 PR Few-electron double dotTransport through dots J.M. Elzerman et al., PRB 67, R161308 (2003) Peak height  1 pA 2 pA 70 pA

  36. Tunnel process is stochastic out out DIQPC (nA) in Time(ms) Time(ms)

  37. G ~ (60 ms)-1 G ~ (230 ms)-1 Increase tunnelbarrier Histograms tunnel time DI QPC [a.u.]

  38. tread twait thold 0.5 1.0 More spin-down traces 2 DIQPC (nA) 1 0 0 1.5 Time (ms)

  39. Read-out characterization spin: outcome: 1-a “up”  a b “down”  1-b

  40. 2 1 DIQPC (nA) 0 0 0.5 1.0 1.5 Time (ms) Characterization: a = Pr [“down” if ] p(1- b - a) exp(- t / T1) +a Spin down fraction 1.0 0.8 a Waiting time (ms) 0.6 0.4 0.2 0.0 0.6 0.8 1.0 Threshold (nA)

  41. Characterization: b = Pr [“up” if ] b1 = Pr [ flips before tunneling ] 1-b = (1-b1)(1-b2) + ab1 1/T1 1 = 1/T1+ G 1 + GT1 1.0 1-b2 0.8 b2= Pr [ miss step ] 0.6 a 1-b 0.4 1 DIQPC (nA) 0.2 0.0 0 0.6 0.8 1.0 Threshold (nA) Time (ms)

  42. Finding the spin read-out regime

  43. gl = gd need glgd N=2 Etriplet > Esinglet gl exchange enhanced (2 DEG, Englert et al, von Klitzing et al) (Tarucha et al, Loss et al) Alternative spin read-out schemes (2) EF Vandersypen et al, Proc. MQC02, see quant-ph/0207059

  44. Alternative spin read-out schemes | = (| - |)+(| + |) = |S + |T0 Engel et al, PRL, to appear (cond-mat/0309023)See also: Ono et al, Science, 2002

  45. Weakly coupled dots dIQPC/dVPR -1000 30 40 20 10 B// = 6 Tesla 00 31 21 11 42 01 32 Right gate (mV) 22 12 02 33 23 13 03 34 24 14 04 -867 Left gate (mV) -900 -1100 QPC gate (mV) -1108 -800

  46. Strongly coupled dots -1167 dIQPC/dVPR B// = 6 Tesla Right gate (mV) 00 -933 Left gate (mV) -967 -1167 QPC gate (mV) -1000 -700

  47. -0.96 0 100 1 2 dip height (%) 3 4 VR (V) 5 6 0 t (ms) 0 370 7 8 2 f = 4.17 kHz 5 4 6 3 7 -0.76 VM (V) -1.07 -1.40 Electron response reveals tunnel rate t = 15 ms 45 lock-in signal (arb.units) 90 180 300 -1.12 -1.13 VM (V) • Electron response (dip) disappears for high frequencies (small t) • Dip half-developed when Gtp • Top: barrier to drain closed • Right: barrier to reservoir closed • Middle: both closed

  48. Singlet-triplet and Zeeman for N = 2 10 10 DEST VP (mV) VP (mV) N = 2 N = 1 N = 2 N = 1 f = 385 Hz f = 1.538 kHz 1 1 -1.160 -1.160 -1.175 -1.175 VM (V) VM (V) Geff G S S

More Related