Superconducting quantum interference device with frequency-dependent damping: Readout of flux qubits

Robertson, T. L.; Plourde, B. L. T.; Hime, T.; Linzen, S.; Reichardt, P. A.; Wilhelm, Frank K.; Clarke, John

doi:10.1103/physrevb.72.024513

Cited by 21 publications

(28 citation statements)

References 25 publications

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“…As the rolloffs are very soft, there is no straightforward mapping onto a very simple model and we have to accept that the dynamics get more complicated and contain a frequency-dependent mass and friction as well as time-correlated noise, all of which gives rise to rich physics (Robertson et al, 2005).…”

Section: Oscillator Bath Models For Josephson Junction Devicesmentioning

confidence: 99%

“…In order to emphasize these general observations, let us investigate the super-Ohmic case with q ≥ 3. Such spectral functions can be realized in electronic circuits by RC-series shunts (Robertson et al, 2005), they also play a significant role in describing phonons. For q > 3, the exponential component vanishes, 1/T 2 = 0 and v q = exp[−2α q Γ(q −1)].…”

Section: Pure Dephasing and The Independent Boson Modelmentioning

confidence: 99%

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Superconducting Qubits II: Decoherence

Wilhelm

Storcz²,

Hartmann³

et al.

Manipulating Quantum Coherence in Solid State Systems

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Section: Oscillator Bath Models For Josephson Junction Devicesmentioning

confidence: 99%

Section: Pure Dephasing and The Independent Boson Modelmentioning

confidence: 99%

Superconducting Qubits II: Decoherence

Wilhelm

Storcz²,

Hartmann³

et al.

Manipulating Quantum Coherence in Solid State Systems

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“…The reliable identification of the quantum state occupation probability of a qubit with high fidelity without introducing detrimental system complexity has been at the center of attention in the design and operation of superconducting qubits in recent years [1][2][3][4]. Over the years these trade-offs were optimized for various types of qubits to enhance overall qubit performance [5][6][7].…”

Section: Pacs Numbersmentioning

confidence: 99%

Readout for phase qubits without Josephson junctions

Steffen

Kumar

DiVincenzo

et al. 2010

Applied Physics Letters

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We present a novel readout scheme for phase qubits which eliminates the read-out SQUID so that the entire qubit and measurement circuitry only requires a single Josephson junction. Our scheme capacitively couples the phase qubit directly to a transmission line and detects its state after the measurement pulse by determining a frequency shift observable in the forward scattering parameter of the readout microwaves. This readout is extendable to multiple phase qubits coupled to a common readout line and can in principle be used for other flux biased qubits having two quasi-stable readout configurations. PACS numbers:The reliable identification of the quantum state occupation probability of a qubit with high fidelity without introducing detrimental system complexity has been at the center of attention in the design and operation of superconducting qubits in recent years [1][2][3][4]. Over the years these trade-offs were optimized for various types of qubits to enhance overall qubit performance [5][6][7]. Although some of these new methods could also apply to the phase qubit, measurement techniques for these qubits have remained largely unchanged. The switching of a two or three Josephson junction SQUID into its normal state remains the main technique to identify the qubit state of a phase qubit [8][9][10].In this letter, we show a novel phase qubit read-out method [11] which eliminates the SQUID and its associated dissipation entirely [3]. By removing the SQUID we also reduce the number of required Josephson junctions from three or four to only a single Josephson junction, thereby dramatically improving the overall device yield.The measurement of phase qubits is typically done in two steps (e.g. [12]). First, the quantum state is "measured" by taking advantage of the potential energy landscape such that post measurement the system is in one of two quasi-stable configuration depending on the quantum state prior to measurement. This step has been demonstrated with large single-shot fidelities and reliable performance [9]. Finally, the qubit is "read out" by identifying which of the quasi-stable configurations the system is in. By convention we refer to these configurations as the left (L) and right (R) configuration. Because the L and R configurations correspond to a large difference of the circulating current in the qubit, the obvious choice has been to flux couple a SQUID to the qubit and detect the current at which a SQUID switches to its voltage state. The configuration, L or R, can be identified with high confidence using the SQUID, usually without significant backaction. Recently, however there has been mounting evidence that the SQUID does indeed limit qubit coherence times or at least drastically impacts the repetition rate of the experiment [3,13]. Because the L and R configurations in a phase qubit have dramatically different resonance frequencies we propose to identify the system configuration by probing the qubit with microwave pulses using dispersive techniques [5][6][7]. We estimate that the correct ide...

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“…For this reason, environment-induced decoherence has been and is still a main obstacle to the practical application of superconducting qubits in quantum computation. [2,13,14,15,16] The environment-induced decoherence of superconducting qubits has been extensively studied both theoretically [15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33] and experimentally [2,8,13,21,25,34,35,36,37,38,39,40] in the absence of ac driving fields (free decay). Quite a few proposals, such as dynamical decoupling, [41,42,43,44,45,46,47,48] decoherence free subspaces, [49,50,51,52] spin echoes, …”

Section: Introductionmentioning

confidence: 99%

Relaxation and decoherence in a resonantly driven qubit

Zhou

Chu

Han

2008

J. Phys. B: At. Mol. Opt. Phys.

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Relaxation and decoherence of a qubit coupled to environment and driven by a resonant ac field are investigated by analytically solving Bloch equation of the qubit. It is found that the decoherence of a driven qubit can be decomposed into intrinsic and field-dependent ones. The intrinsic decoherence time equals to the decoherence time of the qubit in free decay while the fielddependent decoherence time is identical with the relaxation time of the qubit in driven oscillation. Analytical expressions of the relaxation and decoherence times are derived and applied to study a microwave-driven SQUID flux qubit. The results are in excellent agreement with those obtained by numerically solving the master equation. The relations between the relaxation and decoherence times of a qubit in free decay and driven oscillation can be used to extract the decoherence and thus dephasing times of the qubit by measuring its population evolution in free decay and resonantly driven oscillation.

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Superconducting quantum interference device with frequency-dependent damping: Readout of flux qubits

Cited by 21 publications

References 25 publications

Superconducting Qubits II: Decoherence

Superconducting Qubits II: Decoherence

Readout for phase qubits without Josephson junctions

Relaxation and decoherence in a resonantly driven qubit

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