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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!