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SQUID Based Quantum Bits

SQUID Based Quantum Bits. James McNulty. What’s a SQUID?. Superconducting Quantum Interference Device. How A SQUID Works. Flux Quanta Current density zero! (Meissner Effect) Unit of flux: Josephson Junction Tunneling : Phase difference: Current Produced with no Voltage!

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SQUID Based Quantum Bits

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  1. SQUID Based Quantum Bits James McNulty

  2. What’s a SQUID? • Superconducting • Quantum • Interference • Device

  3. How A SQUID Works • Flux Quanta • Current density zero! (Meissner Effect) • Unit of flux: • Josephson Junction • Tunneling : • Phase difference: • Current Produced with no Voltage! • Due to phase difference Superconducting ring

  4. How A SQUID Works • Two Josephson Junctions • Phase difference around loop • Supercurrent • Maximum Value • Creates interference pattern • Very sensitive to changes In flux

  5. Flux Qubits SC Ring • A superconducting ring with a Josephson Junction • External source of flux • Behaves as particle in double potential well • Each well represents supercurrents in opposite directions: CW , CCW • At Superposition state of symmetric anti SQUID U Φ C.H. van der Wal, et al. Quantum superposition of macroscopic persistent-current states. Science290(5492):773-777, 2000.

  6. Flux Qubits Φext= Φ0 /2 • Irradiate JJ with microwaves • 1-10 GHz to transition between states • Change qubit from to and vice versa when • Higher states not accessible Clarke, J., Wilhelm, F.K. Superconducting Quantum Bits, Nature 453,1031-1042(2008).

  7. Flux Qubits • SQUID detects the flux produced in qubit • Averages current (flux) from qubit over multiple trials • As Flux moves away from state switching requires more energy F(GHz) C.H. van der Wal, et al. Quantum superposition of macroscopic persistent-current states. Science290(5492):773-777, 2000.

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