Spin Readout with Superconducting Circuits

April 27th, 2011N. Antler

R. Vijay, E. Levenson-Falk, I. Siddiqi

MotivationNanobridge SQUID Magnetometer:• Spin Physics:

– Dynamics– Coherence times w/ conc.– Spin-Substrate Interaction

• Applications:– Nanoscale ESR/NMR

NV Centers in DiamondCr7Ni (S=1/2)

Bi in Si-28

What is a SQUID?Superconducting QUantum Interference Device

S

S I ()

• Insulator (tunnel junction)

• Constriction (nanobridge junction)

Josephson Junctions

LJ and I0 relation is more complex.

DC SQUID• Loop interrupted by two Josephson Junctions.• SQUID transduces magnetic flux to phase modulation.

FoF

1 2 3

Tunnel Junction DC SQUIDLJ >> LLOOP

IC (Φ) LJ (Φ)

Flux TransductionNon-linear ResonatorResonator Phase

Readout Scheme

Microwave and Cryogenic Setup

Detector Sensitivity

• Low flux noise:0.03 μΦ0/Hz1/2

• Bandwidth > 10 MHz• Ideal for “single” spin

magnetometry

Bulk Spin SensitivityImplanted Spins:• 104 Bi atoms/μm2 at 40 nm

peak depth

Φloop (DC) ~ 27 μΦ0

SNR ~ 3.4• 100 KHz bandwidth (10 μs

integration time)

Bulk NV Centers:• Plane of 5.5x1016 NV

Centers/cm^3, 1 μm above

Φloop (DC) ~ 7 μΦ0

SNR ~ 1

Single Bohr Magneton Sensitivity

L = 1 μm

D = 1 to 103 nm

Single Spin Sensitivity:• 180 nm at 1 Hz BW• 2 nm at 10 kHz BW

Conclusion

• Nanobridge SQUIDs are a good candidate for detecting small #s of spins

Next Steps:• Continue looking for signature of spins• Vary spin density and measure relaxation

times• Attempt pulsed excitation and control

References

• R. Vijay, E. M. Levenson-Falk, D. H. Slichter, and I. Siddiqi, Approaching ideal weak link behavior with three dimensional aluminum nanobridges, Applied Physics Letters 96(22), 223112 (2010)

• M. Hatridge, R. Vijay, D. H. Slichter, J. Clarke, and I. Siddiqi, Dispersive magnetometry with a quantum limited SQUID parametric amplifier, Phys. Rev. B 83(13), 134501 (Apr 2011).

• R. Vijay, E. Levenson-Falk, N. Antler, and I. Siddiqi, in preparation (2011)

Acknowledgements• Many thanks to all the members of QN

• This work supported by: NSF Center for E3S, NSF GRFP and NDSEG

Parametric Amplifier

• Drive the resonator such that it is just below the regime where it bifurcates.

• Transduction of flux + parametric amplification!