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SUMMARY:Coherence and coupling of GaAs two-electron spin qubits - Prof. He
 ndrik Bluhm\, RWTH Aachen\, Germany
DTSTART:20120322T141500Z
DTEND:20120322T151500Z
UID:TALK37131@talks.cam.ac.uk
CONTACT:Kimberly Cole
DESCRIPTION:Semiconductor spin qubits are promising candidates for quantum
  computation because of their slow decoherence and potential for scalabili
 ty.  All fundamental single qubit operations have been demonstrated for Ga
 As based spin qubits\, but they suffer from decoherence due to hyperfine c
 oupling to nuclear spins. We have developed effective techniques to mitiga
 te this decoherence channel for two-electron spin qubits in double quantum
  dots.\n\nBy repeatedly inverting the qubit in a way that decouples its ev
 olution from the fluctuations of the nuclear spin bath\, its coherence tim
 e can be extended to more than 200 us\, two orders of magnitude longer tha
 n previously shown. Alternatively\, operating the qubit as a feedback loop
  that controls the nuclear bath also enhances the coherence time and enabl
 es universal single qubit control with greatly improved gate fidelities.\n
 \nHaving achieved good single qubit control\, a fundamental milestones is 
 to couple qubits in order to generate entanglement.  We demonstrate a prot
 ocol to implement two-qubit gates using the Coulomb interaction between ad
 jacent double dots while decoupling both qubits from slow electrical fluct
 uations.  These results indicate that Bell states can be created with suff
 icient fidelity to demonstrate entanglement.\n
LOCATION:Small Lecture Theatre\, Cavendish Laboratory\, Department of Phys
 ics
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