Resonant Readout of a Persistent Current Qubit

Boquien, M.; Oliver, William; Orlando, Terry P.; Berggren, Karl K.

doi:10.1109/tasc.2005.850077

Cited by 12 publications

(16 citation statements)

References 9 publications

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“…The phenomenon of bistability has been recently observed in an electrical circuit biasing a Josephson junction 4,22 . Its operation as an amplifier has been studied 3 and used to measure a superconducting qubit 5,23 .…”

Section: Further Discussionmentioning

confidence: 99%

Microwave bifurcation of a Josephson junction: Embedding-circuit requirements

et al. 2007

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A Josephson tunnel junction which is RF-driven near a dynamical bifurcation point can amplify quantum signals. The bifurcation point will exist robustly only if the electrodynamic environment of the junction meets certain criteria. In this article we develop a general formalism for dealing with the non-linear dynamics of Josephson junction embedded in an arbitrary microwave circuit. We find sufficient conditions for the existence of the bifurcation regime: a) the embedding impedance of the junction need to present a resonance at a particular frequency ωR, with the quality factor Q of the resonance and the participation ratio p of the junction satisfying Qp ≫ 1, b) the drive frequency should be low frequency detuned away from ωR by more than √ 3ωR/(2Q).

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Section: Further Discussionmentioning

confidence: 99%

Microwave bifurcation of a Josephson junction: Embedding-circuit requirements

et al. 2007

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“…Threshold detection looks for the presence or absence of a SQUID voltage, and this constitutes a digital measurement of the qubit state. Alternatively, although not used in these experiments, we have incorporated the SQUID into a resonant circuit and realized qubit readout via the shift in resonance frequency and phase for both the linear and non-linear resonance regimes 61,62 . The "qubit step" is shown in Fig.…”

Section: Introductionmentioning

confidence: 99%

Large-amplitude driving of a superconducting artificial atom

Oliver

Valenzuela

2009

Quantum Inf Process

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Superconducting persistent-current qubits are quantum-coherent artificial atoms with multiple, tunable energy levels. In the presence of large-amplitude harmonic excitation, the qubit state can be driven through one or more of the constituent energy-level avoided crossings. The resulting LandauZener-Stückelberg (LZS) transitions mediate a rich array of quantum-coherent phenomena. We review here three experimental works based on LZS transitions: Mach-Zehnder-type interferometry between repeated LZS transitions, microwave-induced cooling, and amplitude spectroscopy. These experiments exhibit a remarkable agreement with theory, and are extensible to other solid-state and atomic qubit modalities. We anticipate they will find application to qubit state-preparation and control methods for quantum information science and technology.

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“…The noise decreases by nearly two orders of magnitude as the temperature is increased from 120 to 1200 mK, while the variation of the resonance frequency with temperature over this range agrees well with the standard two-level system ͑TLS͒ model for amorphous dielectrics. Superconducting microresonators are useful for photon detection, [1][2][3][4][5][6][7] coupling to qubits, [8][9][10] superconducting quantum interference device multiplexers, 11,12 and studying basic physics. [13][14][15][16] Such resonators have excess noise 2,17 that is equivalent to a jitter of the resonance frequency, likely caused by two-level tunneling systems ͑TLSs͒ in amorphous dielectrics.…”

mentioning

confidence: 99%

Temperature dependence of the frequency and noise of superconducting coplanar waveguide resonators

Kumar

Gao

Žmuidzinas

et al. 2008

Applied Physics Letters

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We present measurements of the temperature and power dependence of the resonance frequency and frequency noise of superconducting niobium thin-film coplanar waveguide resonators carried out at temperatures well below the superconducting transition ͑T c = 9.2 K͒. The noise decreases by nearly two orders of magnitude as the temperature is increased from 120 to 1200 mK, while the variation of the resonance frequency with temperature over this range agrees well with the standard two-level system ͑TLS͒ model for amorphous dielectrics. These results support the hypothesis that TLSs are responsible for the noise in superconducting microresonators and have important implications for resonator applications such as qubits and photon detectors. 23 have highlighted TLS effects in superconducting microcircuits. While the TLS energy splitting ⌬E has a broad distribution, 22 a resonator with frequency f r is most sensitive to TLS with ⌬E ϳ hf r . The level populations and relaxation rates of such TLS vary strongly at temperatures T ϳ hf r / 2k B , or around 100 mK for the device studied here. Furthermore, such near-resonant TLS may saturate 18 for strong resonator excitation power P w . Hence, measurements of the power and temperature variation of the resonator frequency and noise, as presented in this letter, provide a strong test of the TLS hypothesis.We studied coplanar waveguide ͑CPW͒ quarterwavelength resonators 2,18 fabricated on a high-resistivity ͑ ജ 10 k⍀ cm͒ crystalline silicon substrate by patterning a 200 nm thick niobium film using a photoresist mask and a SF 6 inductively coupled plasma etch. In this device, TLS may be present in the native oxide surface layers on the metal film or substrate. 18 The resonator is capacitively coupled to a CPW feedline ͑Fig. 1͒ that has a 10 m wide center strip and 6 m gaps between the center strip and the ground plane. For the resonator, these dimensions are 5 and 1 m, respectively. The resonator length is 5.8 mm, corresponding to f r = 4.35 GHz. The coupling strength is set lithographically 17,18 ͑see Fig. 1͒ and is characterized by the coupling-limited quality factor Q c =5ϫ 10 5 . The device was cooled using a dilution refrigerator, and its temperature was measured to Ϯ5 mK accuracy using a calibrated RuO 2 thermometer mounted on the copper sample enclosure. The microwave readout ͑Fig. 1͒ uses a standard IQ homodyne mixing technique. 2,17 The IQ mixer's complex output voltage ͑f͒ = I͑f͒ + jQ͑f͒ follows a circular trajectory in the complex plane as the microwave excitation frequency f is varied, 18 and f r and Q r are determined by complex leastsquares fitting of this trajectory to a ten-parameter model:Here ␦x = ͑f − f r ͒ / f r is the fractional frequency offset, S 21 ͑r͒ is the complex forward transmission on resonance, B 0 + B 1 ␦x allows for a linear gain variation, 0 + 1 ␦x allows a similar linear phase variation, and B 2 and 2 specify the output offset voltages of the IQ mixer. The combined noise of the resonator and readout electronics is measured by tuning the synthesi...

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Resonant Readout of a Persistent Current Qubit

Cited by 12 publications

References 9 publications

Microwave bifurcation of a Josephson junction: Embedding-circuit requirements

Microwave bifurcation of a Josephson junction: Embedding-circuit requirements

Large-amplitude driving of a superconducting artificial atom

Temperature dependence of the frequency and noise of superconducting coplanar waveguide resonators

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