1. Spin Readout with Superconducting Circuits April 27 th, 2011 N. Antler R. Vijay, E. Levenson-Falk, I. Siddiqi

2. Motivation Nanobridge SQUID Magnetometer: Spin Physics: – Dynamics – Coherence times w/ conc. – Spin-Substrate Interaction Applications: – Nanoscale ESR/NMR NV Centers in Diamond Cr 7 Ni (S=1/2) Bi in Si-28

3. What is a SQUID? Superconducting QUantum Interference Device

4. S S  I (  ) Insulator (tunnel junction) Constriction (nanobridge junction) Josephson Junctions L J and I 0 relation is more complex.

5. DC SQUID Loop interrupted by two Josephson Junctions. SQUID transduces magnetic flux to phase modulation.  o  123 Tunnel Junction DC SQUID L J >> L LOOP I C (Φ)  L J (Φ)

6. Flux Transduction Non-linear Resonator Resonator Phase

7. Readout Scheme

9. Microwave and Cryogenic Setup

10. Detector Sensitivity Low flux noise: 0.03 μΦ 0 /Hz 1/2 Bandwidth > 10 MHz Ideal for “single” spin magnetometry

11. Bulk Spin Sensitivity Implanted Spins: 10 4 Bi atoms/ μ m 2 at 40 nm peak depth Φ loop (DC) ~ 27 μΦ 0 SNR ~ 3.4 100 KHz bandwidth (10 μs integration time) Bulk NV Centers: Plane of 5.5x10 16 NV Centers/cm^3, 1 μ m above Φ loop (DC) ~ 7 μΦ 0 SNR ~ 1

12. Single Bohr Magneton Sensitivity L = 1 μm D = 1 to 10 3 nm Single Spin Sensitivity: 180 nm at 1 Hz BW 2 nm at 10 kHz BW

13. 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

14. 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)

15. Acknowledgements Many thanks to all the members of QN This work supported by: NSF Center for E3S, NSF GRFP and NDSEG

16. Parametric Amplifier Drive the resonator such that it is just below the regime where it bifurcates. Transduction of flux + parametric amplification!