Frequency division multiplexing readout and simultaneous manipulation of an array of flux qubits

Jerger, Markus; Poletto, Stefano; Macha, P.; Hübner, Uwe; Il’ichev, E.; Ustinov, A. V.

doi:10.1063/1.4739454

Cited by 72 publications

(60 citation statements)

References 8 publications

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“…While quasiparticles are the main candidate for energy relaxation, we do not exclude other potential sources, in particular loss due to amorphous interfaces and surfaces [25]. We note that lower energy relaxation times, in the 0.5 − 1 µs range, were obtained in previous experiments with aluminum flux qubits coupled to superconducting resonators made of niobium [16,17]. Possible reasons for the longer relaxation times in our experiment include a reduction of quasiparticle induced relaxation, due to using an all aluminum circuit, and a reduction of surface/interface loss arising due to the different processing prior to deposition of the qubit layer.…”

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confidence: 92%

Flux qubits in a planar circuit quantum electrodynamics architecture: Quantum control and decoherence

et al. 2016

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We report experiments on superconducting flux qubits in a circuit quantum electrodynamics (cQED) setup. Two qubits, independently biased and controlled, are coupled to a coplanar waveguide resonator. Dispersive qubit state readout reaches a maximum contrast of 72 %. We find intrinsic energy relaxation times at the symmetry point of 7 µs and 20 µs and levels of flux noise of 2.6 µΦ0/ √ Hz and 2.7 µΦ0/ √ Hz at 1 Hz for the two qubits. We discuss the origin of decoherence in the measured devices. These results demonstrate the potential of cQED as a platform for fundamental investigations of decoherence and quantum dynamics of flux qubits.PACS numbers: 85.25. Cp, 42.50.Dv , 03.67.Lx, 74.78.Na Superconducting qubits are one of the main candidates for the implementation of quantum information processing [1] and a rich testbed for research in quantum optics, quantum measurement, and decoherence [2]. Among various types of superconducting qubits, flux-type superconducting qubits have unique features. Strong and tunable coupling to microwave fields enables fundamental investigations in quantum optics [3][4][5] and relativistic quantum mechanics [6]. The large magnetic dipole moment is a key ingredient in flux noise measurements [5], sensitive magnetic field measurements [8], microwave-optical interfaces [9], and hybrid systems formed with nanomechanical resonators [10]. Finally, flux qubits have a large degree of anharmonicity which is an advantage for fast quantum control [11]. Progress on these diverse research avenues has been hampered by relatively low and irreproducible coherence times compared to other types of superconducting qubits.In the last decade, circuit quantum electrodynamics (cQED) [12,13] has become increasingly popular. In cQED, resonators provide a controlled electromagnetic environment protecting qubits from energy relaxation. In addition, resonators are used for qubit state measurement [2] and as quantum buses for qubit-qubit coupling [15]. In this letter, we present an implementation of cQED with flux qubits strongly coupled to a superconducting coplanar waveguide resonator. The qubits and the resonator are made of aluminum. Local biasing and control lines provide a mean to implement fast single qubit gates as well as controlled two-qubit interactions. We measure energy relaxation times around 10 µs, an improvement over previous experiments with flux qubits coupled to coplanar waveguide resonators [16,17], and comparable with the longest measured to date on flux qubits [5,18]. We characterize in detail the decoherence of the flux qubits coupled to the resonator. Based on decoherence measurements, we extract levels of flux noise of 2.6 µΦ 0 / √ Hz and 2.7 µΦ 0 / √ Hz at 1 Hz for the two qubits. We also present a spectroscopic measurement of a resonator-mediated qubit-qubit coupling, which is relevant for implementation of two-qubit gates. These results demonstrate the versatility of cQED with flux qubits, and its potential for further understanding and improvements of decoherence of these qubits.T...

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confidence: 92%

Flux qubits in a planar circuit quantum electrodynamics architecture: Quantum control and decoherence

et al. 2016

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“…In this study we investigate the driven dynamics of a strongly interacting system composed of a superconducting flux qubit [15,16] and a coplanar waveguide (CPW) microwave cavity [9,14,[17][18][19][20][21]. The nonlinear cavity response [22][23][24][25][26][27][28][29][30][31][32][33][34][35][36] is measured as a function of the magnetic flux that is applied to the qubit.…”

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confidence: 99%

Superharmonic resonances in a strongly coupled cavity-atom system

Buks¹,

Deng²,

Orgazzi³

et al. 2016

Phys. Rev. A

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We study a system consisting of a superconducting flux qubit strongly coupled to a microwave cavity. The fundamental cavity mode is externally driven and the response is investigated in the weak nonlinear regime. We find that near the crossing point, at which the resonance frequencies of the cavity mode and qubit coincide, the sign of the Kerr coefficient changes, and consequently the type of nonlinear response changes from softening to hardening. Furthermore, the cavity response exhibits superharmonic resonances when the ratio between the qubit frequency and the cavity fundamental mode frequency is tuned close to an integer value. The nonlinear response is characterized by the method of intermodulation and both signal and idler gains are measured. Cavity quantum electrodynamics (CQED) [1] is the study of the interaction between photons confined in a cavity and atoms (natural or artificial). The interaction is commonly described by the Rabi or Jaynes-Cummings Hamiltonians [2], and it has been the subject of numerous theoretical and experimental investigations. An on-chip CQED system can be realized by integrating a Josephson qubit [3][4][5] (playing the role of an artificial atom) with a superconducting microwave resonator (cavity) [6][7][8]. Superconducting CQED systems have generated a fast growing interest due to the possibility to reach the strong [7] and ultra-strong [9, 10] coupling regimes, and due to potential applications in quantum information processing [4,[11][12][13].In this study we investigate the driven dynamics of a strongly interacting system composed of a superconducting flux qubit [15,16] and a coplanar waveguide (CPW) microwave cavity [9,14,[17][18][19][20][21]. The nonlinear cavity response [22][23][24][25][26][27][28][29][30][31][32][33][34][35][36] is measured as a function of the magnetic flux that is applied to the qubit. At weak driving and when the ratio between the qubit frequency and the cavity fundamental mode frequency is tuned close to the value ω a /ω c = 1 the common Jaynes-Cummings resonance, which henceforth is referred to as the primary resonance, is observed. With stronger driving, however, and when the ratio ω a /ω c is tuned close to integer values larger than unity, superharmonic resonances appear in the measured response. Intermodulation (IMD) measurements are employed to characterize the nonlinear response [37][38][39]. The results are compared with the predictions of a theoretical model, which is based on linearization of the equations of motion that govern the dynamics of the CQED system under study.

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“…1(a) and 1(b)]. The chip layout and the design philosophy of microwave elements mirror those of superconducting quantum processors [21][22][23]. In the absence of Josephson dynamics, the fundamental λ=2 resonance mode is characterized by the resonance frequency f ð0Þ r ¼ 5.6681 GHz, the internal and coupling quality factors Q ð0Þ i ¼ 3400 and Q c ¼ 760, respectively, and impedance Z lc ¼ ð2=πÞZ r , where Z r ¼ 30 Ω is the characteristic impedance of the waveguide.…”

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confidence: 99%

Dispersive Thermometry with a Josephson Junction Coupled to a Resonator

Saira¹,

Zgirski

Viisanen³

et al. 2016

Phys. Rev. Applied

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We embed a small Josephson junction in a microwave resonator that allows simultaneous dc biasing and dispersive readout. Thermal fluctuations drive the junction into phase diffusion and induce a temperaturedependent shift in the resonance frequency. By sensing the thermal noise of a remote resistor in this manner, we demonstrate primary thermometry in the range of 300 mK to below 100 mK, and highbandwidth (7.5 MHz) operation with a noise-equivalent temperature of better than 10 μK= ffiffiffiffiffiffi Hz p . At a finite bias voltage close to a Fiske resonance, amplification of the microwave probe signal is observed. We develop an accurate theoretical model of our device based on the theory of dynamical Coulomb blockade.

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Frequency division multiplexing readout and simultaneous manipulation of an array of flux qubits

Cited by 72 publications

References 8 publications

Flux qubits in a planar circuit quantum electrodynamics architecture: Quantum control and decoherence

Flux qubits in a planar circuit quantum electrodynamics architecture: Quantum control and decoherence

Superharmonic resonances in a strongly coupled cavity-atom system

Dispersive Thermometry with a Josephson Junction Coupled to a Resonator

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