Universität Stuttgart, 9. October 2004

contents

• past deliverables and present work

• decoherence in solid state N/P@C60

HMI FU-Berlin

http://www.hmi.de/people/carola.meyer/Dissertation

(defence: 14. November)

Universität Stuttgart, 9. October 2004

material supply (D 1.1)

Small amounts (~ 5 mg) of quality 10-3 have been supplied to Uni Dortmund

Micro resonator:

Small amounts (~ 1 mg) of quality 10-4 to Uni Stuttgart

stability tests:

average amounts (~ 0.5 g) of quality 10-4 to Uni Dublin

enrichment:

No further requests have been received from the partners

Universität Stuttgart, 9. October 2004

N@C60 - C60 dimer (D 1.2)

1.0

0.8

0.6

0.4

0.2

0.0

ES

R-S

igna

l (ar

b. u

nits

)

347.5347.0346.5346.0345.5345.0

magnetic field (mT)

K.-P. Dinse

P. Jakes

Universität Stuttgart, 9. October 2004

present/future work

D 1.3 (month 12): highly enriched material (>20%)

• CTA (BmBF) will start middle of October

production and enrichment will stay at HMI until March ‘04

D 1.4 (month 15): diluted doubly-filled dimers

• Postdoc (BmBF) started in September• build-up the production of mechanically synthesised dimer• start chemical route towards dimer• move to FU-Berlin

Universität Stuttgart, 9. October 2004

spin-lattice relaxation

modulation of local B0 causes relaxation

Hrel = Hhf + Hfs + Hdip = IAS + SDS + STR

• strength of interaction

relaxation rate is determined by:

• phonons (DOS), which modulate the interaction

A ~ 140 MHz

D ~ 14 MHz

T ~ 440 kHz

P@C60

A ~ 15 MHz

D ~ 0.5 MHz

T ~ 440 kHz

N@C60

Universität Stuttgart, 9. October 2004

relaxation paths

10-1

100

101

102

103

104

105

106

relax

ation

rate

(Hz)

4 6 810

2 4 6 8100

2 4

temperature (K)

two relaxation rates can be resolved

Universität Stuttgart, 9. October 2004

harmonic oscillator

10-1

100

101

102

103

104

105

106

relax

ation

rate

(Hz)

4 6 810

2 4 6 8100

2 4

temperature (K)

10-6

10-5

10-4

10-3

10-2

10-1

100

a2/(2h) 2(M

Hz 2)

138.4

138.2

138.0

137.8

137.6

137.4

137.2

137.0

hype

rfin

e sp

littin

g (M

Hz)

300250200150100500

temperature (K)

temperature dependence of hyperfine coupling A

T > 35K: harmonic oscillator

T < 35K: acoustic phonons

Universität Stuttgart, 9. October 2004

T < 35 K

relaxation depends only on spin concentration

model for T1

T > 35 K

relaxation larger for P@C60 than for N@C60

4 6 810

2 4 6 8100

2 4

temperature (K)

10-1

100

101

102

103

104

105

106re

laxat

ionra

te(H

z)P@C60

N@C60

Universität Stuttgart, 9. October 2004

T1 and scalability

for a powder sample with 100% spin concentrationT1 ~ 1 ms

oscillator mode Hint max. coupling strength( )

phonon model

SAI a/2h ~ 140 MHzSDS D/2h ~ 14 MHzinternal oscillatorSTR T/2h ~ 440 kHz

harmonic oscillator

STS' a T/2h ~ 50 MHz STS' b T/2h ~ 1 kHzacoustic phonon STR' T/2h ~ 70 kHz

Debye

a spin concentration 100 %b spin concentration of "Phoenix"

Universität Stuttgart, 9. October 2004

spin-spin relaxation

P@C60

N@C60

~ 50 oscillations at room temperature

number of single qubit operations at room temperature

Universität Stuttgart, 9. October 2004

temperature dependence

N@C60:T2 = 14 µs

10-6

10-5

10-4

10-3

10-2

10-1

100

101

rela

xatio

n tim

e (s

)

4 5 6 710

2 3 4 5 6 7100

2 3 4

temperature (K)

P@C60 powder

P@C60:T2 = 14 µs

Universität Stuttgart, 9. October 2004

T2 and scalability

in a sample with random distribution of electron spins:

• T2 itself is temperature independent

• depends on spin concentration

P@C60/C60 T2

1 x10-4 1 µs

2.4 x10-5 14 µs

1 x10-6 28 µs

• high dilution limit T2 = ?

Universität Stuttgart, 9. October 2004

our qubit in contest

Ladd et al., arXiv:quant-ph/0309164 v1 (23.09.03)

number of single-qubit gates: Rabi

T2 ~ 103number of two-qubit gates: J max T2 ~ 103

for error correction gain one order of magnitude in T2:• measure T2 at spin concentrations as low as possible (signal/noise)

• use pulse sesquences known from NMR for dipolar decoupling

Universität Stuttgart, 9. October 2004

conclusions

even in solid state concept T1 ~ ms (worst case)

measure coupling (T1) on surface

50 Rabi oscillations at room temperature

show short two-qubit gates

spin-spin relaxation up to T2 = 28 µs

measure T2 in high dilution limit