Implementing gates in quantum dot spin qubits
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Transcript of Implementing gates in quantum dot spin qubits
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Implementing gates in quantum dot spin
qubitsTomáš Bzdušek
QSIT student presentation28th november 2011
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Reminder◦What is a (double) quantum dot?◦What was discussed on the lecture?
The talk itself◦Energy diagram of DQD.◦Dephasing of a qubit◦SWAP operation◦Spin Echo
Outline
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What was discussed on the lecture?
(a rather long reminder)
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Double quantum dot
Strong magnetic
field
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Lecture outline
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Fermi level
Applyingproper voltage
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Read-out done using quantum point contact (QPC)
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Lecture overview
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Energy Diagram of a Double Quantum Dot
It brings some general ideas.
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Spin-less particle in double well
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Spin-less particle in double well
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Energy diagram of a double quantum dot (1)
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Weak coupling between (0,2)S and (1,1)T+.
Energy diagram of a double quantum dot (2)
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In this region, the state effectively described in S – T0 subspace,
Effective hamiltonian:
Energy diagram of a double quantum dot (3)
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Far left = deep in (1,1) region, . Eigenstates of subspace are and !
Energy diagram of a double quantum dot (3)
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The logical qubit
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Qubit manipulation
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Qubit manipulation
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Dephasing TimeExperiment #1
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Fast and wait
Measuring dephasing time
fast
or... ?
Fast backwards
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Dephasing time – Results
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Spin EchoExperiment #2
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Spin Echo: State manipulation
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Spin Echo: Theory vs. Experiment
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SWAP OperationExperiment #3
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SWAP operation
fast
adiabatically
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SWAP operation
Fast and wait
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adiabatically
fast
SWAP operation
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SWAP: Theory vs. Experiment
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Summary
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Read-out fidelity ≈ 86 % Dephasing time ≈ 10 ns Echo-coherence time ≈ 1.2 μs
Summary
Thank you for attention!It’s time for your questions.
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Hanson, R; Kouwenhoven, LP; Petta, JR; et al.◦ Spins in few-electron quantum dots◦ Reviews of Modern Physics 79, 1217 (2007)
Petta, JR; Johnson, AC; Taylor, JM; et al.◦ Coherent manipulation of coupled electron spins in
semiconductor quantum dots◦ Science 309, 2180 (2005)
Nowack, K. C.; Shafiei, M.; Laforest, M.; et al.◦ Single-Shot Correlations and Two-Qubit Gate of
Solid-State Spins◦ Science 333, 1269 (2011)
Special thanks to Arkady Fedorov for his willing advice.
Used literature
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Hello, whoever you are! If you got this far, please send me an email to
tomas(dot)bzdusek(at)gmail(dot)com. I am really curious how many people finds this presentation useful, say, during 5 years after my talk.
However, considering ammount of words used in the slides, I think they won’t help you much, if you did not attend my talk.
I wish you good luck anyway, whatever reason has led you here.
(ancient words of the author, 5th December 2011)
Final note