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Selective darkening of degenerate transitions for implementing quantum controlled-NOT gates

De Groot, P.C. (author), Ashhab, S. (author), Lupascu, A. (author), DiCarlo, L. (author), Nori, F. (author), Harmans, C.J.P.M. (author), Mooij, J.E. (author)

We present a theoretical analysis of the selective darkening method for implementing quantum controlled-NOT (CNOT) gates. This method, which we have recently proposed and demonstrated, consists of driving two transversely coupled quantum bits (qubits) with a driving field that is resonant with one of the two qubits. For specific relative...

journal article 2012

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Initialization by Measurement of a Superconducting Quantum Bit Circuit

Riste, D. (author), Van Leeuwen, J.G. (author), Ku, H.S. (author), Lehnert, K.W. (author), DiCarlo, L. (author)

We demonstrate initialization by joint measurement of two transmon qubits in 3D circuit quantum electrodynamics. Homodyne detection of cavity transmission is enhanced by Josephson parametric amplification to discriminate the two-qubit ground state from single-qubit excitations nondestructively and with 98.1% fidelity. Measurement and...

journal article 2012

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Feedback Control of a Solid-State Qubit Using High-Fidelity Projective Measurement

Riste, D. (author), Bultink, C.C. (author), Lehnert, K.W. (author), DiCarlo, L. (author)

We demonstrate feedback control of a superconducting transmon qubit using discrete, projective measurement and conditional coherent driving. Feedback realizes a fast and deterministic qubit reset to a target state with 2.4% error averaged over input superposition states, and allows concatenating experiments more than 10 times faster than by...

journal article 2012

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Probing Dynamics of an Electron-Spin Ensemble via a Superconducting Resonator

Ranjan, V. (author), De Lange, G. (author), Schutjens, R. (author), Debelhoir, T. (author), Groen, J.P. (author), Szombati, D. (author), Thoen, D.J. (author), Klapwijk, T.M. (author), Hanson, R. (author), DiCarlo, L. (author)

We study spin relaxation and diffusion in an electron-spin ensemble of nitrogen impurities in diamond at low temperature (0.25–1.2 K) and polarizing magnetic field (80–300 mT). Measurements exploit field-controlled coupling of the ensemble to two modes of a transmission-line resonator. The observed temperature-independent spin relaxation time...

journal article 2013

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Millisecond charge-parity fluctuations and induced decoherence in a superconducting transmon qubit

Riste, D. (author), Bultink, C.C. (author), Tiggelman, M.J. (author), Schouten, R.N. (author), Lehnert, K.W. (author), DiCarlo, L. (author)

The tunnelling of quasiparticles across Josephson junctions in superconducting quantum circuits is an intrinsic decoherence mechanism for qubit degrees of freedom. Understanding the limits imposed by quasiparticle tunnelling on qubit relaxation and dephasing is of theoretical and experimental interest, particularly as improved understanding of...

journal article 2013

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Partial-Measurement Backaction and Nonclassical Weak Values in a Superconducting Circuit

Groen, J.P. (author), Riste, D. (author), Tornberg, L. (author), Cramer, J. (author), De Groot, P.C. (author), Picot, T. (author), Johansson, G. (author), DiCarlo, L. (author)

We realize indirect partial measurement of a transmon qubit in circuit quantum electrodynamics by interaction with an ancilla qubit and projective ancilla measurement with a dedicated readout resonator. Accurate control of the interaction and ancilla measurement basis allows tailoring the measurement strength and operator. The tradeoff between...

journal article 2013

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Entanglement Genesis by Ancilla-Based Parity Measurement in 2D Circuit QED

Saira, O.P. (author), Groen, J.P. (author), Cramer, J. (author), Meretska, M. (author), De Lange, G. (author), DiCarlo, L. (author)

We present an indirect two-qubit parity meter in planar circuit quantum electrodynamics, realized by discrete interaction with an ancilla and a subsequent projective ancilla measurement with a dedicated, dispersively coupled resonator. Quantum process tomography and successful entanglement by measurement demonstrate that the meter is...

journal article 2014

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Reversing Quantum Trajectories with Analog Feedback

De Lange, G. (author), Riste, D. (author), Tiggelman, M.J. (author), Eichler, C. (author), Tornberg, L. (author), Johansson, G. (author), Wallraff, A. (author), Schouten, R.N. (author), DiCarlo, L. (author)

We demonstrate the active suppression of transmon qubit dephasing induced by dispersive measurement, using parametric amplification and analog feedback. By real-time processing of the homodyne record, the feedback controller reverts the stochastic quantum phase kick imparted by the measurement on the qubit. The feedback operation matches a model...

journal article 2014

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Reducing intrinsic loss in superconducting resonators by surface treatment and deep etching of silicon substrates

Bruno, A. (author), De Lange, G. (author), Asaad, S. (author), Van der Enden, K.L. (author), Langford, N.K. (author), DiCarlo, L. (author)

We present microwave-frequency NbTiN resonators on silicon, systematically achieving internal quality factors above 1?M in the quantum regime. We use two techniques to reduce losses associated with two-level systems: an additional substrate surface treatment prior to NbTiN deposition to optimize the metal-substrate interface and deep reactive...

journal article 2015

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High-Kinetic-Inductance Superconducting Nanowire Resonators for Circuit QED in a Magnetic Field

Samkharadze, Nodar (author), Bruno, A. (author), Scarlino, P. (author), Zheng, G. (author), Divincenzo, D.P. (author), DiCarlo, L. (author), Vandersypen, L.M.K. (author)

We present superconducting microwave-frequency resonators based on NbTiN nanowires. The small cross section of the nanowires minimizes vortex generation, making the resonators resilient to magnetic fields. Measured intrinsic quality factors exceed 2×105 in a 6-T in-plane magnetic field and 3×104 in a 350-mT perpendicular magnetic field....

journal article 2016

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Active Resonator Reset in the Nonlinear Dispersive Regime of Circuit QED

Bultink, C.C. (author), Rol, M.A. (author), O'Brien, T.E. (author), Fu, X. (author), Dikken, B.C.S. (author), Dickel, C. (author), Vermeulen, R.F.L. (author), de Sterke, J.C. (author), Bruno, A. (author), Schouten, R.N. (author), DiCarlo, L. (author)

We present two pulse schemes to actively deplete measurement photons from a readout resonator in the nonlinear dispersive regime of circuit QED. One method uses digital feedback conditioned on the measurement outcome, while the other is unconditional. In the absence of analytic forms and symmetries to exploit in this nonlinear regime, the...

journal article 2016

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Scalable Quantum Circuit and Control for a Superconducting Surface Code

Versluis, R. (author), Poletto, S. (author), Khammassi, N. (author), Tarasinski, B.M. (author), Haider, S.N. (author), Michalak, D.J. (author), Bruno, A. (author), Bertels, K.L.M. (author), DiCarlo, L. (author)

We present a scalable scheme for executing the error-correction cycle of a monolithic surface-code fabric composed of fast-flux-tunable transmon qubits with nearest-neighbor coupling. An eight-qubit unit cell forms the basis for repeating both the quantum hardware and coherent control, enabling spatial multiplexing. This control uses three...

journal article 2017

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Restless Tuneup of High-Fidelity Qubit Gates

Rol, M.A. (author), Bultink, C.C. (author), O'Brien, T.E. (author), De Jong, S. R. (author), Theis, L. S. (author), Fu, X. (author), Lüthi, F. (author), Vermeulen, R.F.L. (author), de Sterke, J.C. (author), Bruno, A. (author), Deurloo, D. (author), Schouten, R.N. (author), Wilhelm, FK (author), DiCarlo, L. (author)

We present a tuneup protocol for qubit gates with tenfold speedup over traditional methods reliant on qubit initialization by energy relaxation. This speedup is achieved by constructing a cost function for Nelder-Mead optimization from real-time correlation of nondemolition measurements interleaving gate operations without pause. Applying the...

journal article 2017

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An experimental microarchitecture for a superconducting qantum processor

Fu, X. (author), Rol, M.A. (author), Bultink, C.C. (author), van Someren, J. (author), Khammassi, N. (author), Ashraf, I. (author), Vermeulen, R.F.L. (author), de Sterke, J.C. (author), Vlothuizen, W.J. (author), Schouten, R.N. (author), Almudever, Carmen G. (author), DiCarlo, L. (author), Bertels, K.L.M. (author)

Quantum computers promise to solve certain problems that are intractable for classical computers, such as factoring large numbers and simulating quantum systems. To date, research in quantum computer engineering has focused primarily at opposite ends of the required system stack: devising high-level programming languages and compilers to...

conference paper 2017

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Experimentally simulating the dynamics of quantum light and matter at deep-strong coupling

Langford, N.K. (author), Sagastizabal, R.E. (author), Kounalakis, M. (author), Dickel, C. (author), Bruno, A. (author), Lüthi, F. (author), Thoen, David (author), Endo, A. (author), DiCarlo, L. (author)

The quantum Rabi model describing the fundamental interaction between light and matter is a cornerstone of quantum physics. It predicts exotic phenomena like quantum phase transitions and ground-state entanglement in ultrastrong and deep-strong coupling regimes, where coupling strengths are comparable to or larger than subsystem energies....

journal article 2017

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General method for extracting the quantum efficiency of dispersive qubit readout in circuit QED

Bultink, C.C. (author), Tarasinski, B.M. (author), Haandbæk, N. (author), Poletto, S. (author), Haider, S.N. (author), Michalak, D.J. (author), Bruno, A. (author), DiCarlo, L. (author)

We present and demonstrate a general three-step method for extracting the quantum efficiency of dispersive qubit readout in circuit QED. We use active depletion of post-measurement photons and optimal integration weight functions on two quadratures to maximize the signal-to-noise ratio of the non-steady-state homodyne measurement. We derive...

journal article 2018

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Chip-to-chip entanglement of transmon qubits using engineered measurement fields

Dickel, C. (author), Wesdorp, J.J. (author), Langford, N.K. (author), Peiter, S.R. (author), Sagastizabal, R.E. (author), Bruno, A. (author), Criger, D.B. (author), Motzoi, F. (author), DiCarlo, L. (author)

While the on-chip processing power in circuit QED devices is growing rapidly, an open challenge is to establish high-fidelity quantum links between qubits on different chips. Here, we show entanglement between transmon qubits on different cQED chips with 49% concurrence and 73% Bell-state fidelity. We engineer a half-parity measurement by...

journal article 2018

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A Microarchitecture for a Superconducting Quantum Processor

Fu, X. (author), Rol, M.A. (author), Bultink, C.C. (author), van Someren, J. (author), Khammassi, N. (author), Ashraf, I. (author), Vermeulen, R.F.L. (author), de Sterke, J.C. (author), Vlothuizen, W.J. (author), Schouten, R.N. (author), Almudever, Carmen G. (author), DiCarlo, L. (author), Bertels, K.L.M. (author)

This article proposes a quantum microarchitecture, QuMA. Flexible programmability of a quantum processor is achieved by multilevel instructions decoding, abstracting analog control into digital control, and translating instruction execution with non-deterministic timing into event trigger with precise timing. QuMA is validated by several...

journal article 2018

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Evolution of Nanowire Transmon Qubits and Their Coherence in a Magnetic Field

Lüthi, F. (author), Stavenga, T. (author), Enzing, O.W. (author), Bruno, A. (author), Dickel, C. (author), Langford, N.K. (author), Rol, M.A. (author), Jespersen, T. S. (author), Nygård, J. (author), Krogstrup, P. (author), DiCarlo, L. (author)

We present an experimental study of flux- and gate-tunable nanowire transmons with state-of-the-art relaxation time allowing quantitative extraction of flux and charge noise coupling to the Josephson energy. We evidence coherence sweet spots for charge, tuned by voltage on a proximal side gate, where first order sensitivity to switching two...

journal article 2018

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Experimental error mitigation via symmetry verification in a variational quantum eigensolver

Sagastizabal, R.E. (author), Bonet Monroig, X. (author), Singh, Malay (author), Rol, M.A. (author), Bultink, C.C. (author), Fu, X. (author), Ostroukh, V.P. (author), Muthusubramanian, N. (author), Bruno, A. (author), Beekman, M.C. (author), Haider, S.N. (author), O'Brien, T.E. (author), DiCarlo, L. (author)

Variational quantum eigensolvers offer a small-scale testbed to demonstrate the performance of error mitigation techniques with low experimental overhead. We present successful error mitigation by applying the recently proposed symmetry verification technique to the experimental estimation of the ground-state energy and ground state of the...

journal article 2019