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Wafer-scale uniformity of Dolan-bridge and bridgeless Manhattan-style Josephson junctions for superconducting quantum processors

Muthusubramanian, N. (author), Finkel, M. (author), Duivestein, W.J. (author), Zachariadis, C. (author), van der Meer, S.L.M. (author), Veen, H.M. (author), Beekman, M.C. (author), Stavenga, T. (author), Bruno, A. (author), DiCarlo, L. (author)

We investigate die-level and wafer-scale uniformity of Dolan-bridge and bridgeless Manhattan-style Josephson junctions, using multiple substrates with and without through-silicon vias (TSVs). Dolan junctions fabricated on planar substrates have the highest yield and lowest room-temperature conductance spread, equivalent to ∼ 100 M H z in...

journal article 2024

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All-Microwave Leakage Reduction Units for Quantum Error Correction with Superconducting Transmon Qubits

Varbanov, B.M. (author), Finkel, M. (author), Veen, H.M. (author), van der Meer, S.L.M. (author), Valles Sanclemente, S. (author), Muthusubramanian, N. (author), Beekman, M.C. (author), Haider, S.N. (author), Terhal, B.M. (author), DiCarlo, L. (author)

Minimizing leakage from computational states is a challenge when using many-level systems like superconducting quantum circuits as qubits. We realize and extend the quantum-hardware-efficient, all-microwave leakage reduction unit (LRU) for transmons in a circuit QED architecture proposed by Battistel et al. This LRU effectively reduces...

journal article 2023

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Post-fabrication frequency trimming of coplanar-waveguide resonators in circuit QED quantum processors

Valles Sanclemente, S. (author), van der Meer, S.L.M. (author), Finkel, M. (author), Muthusubramanian, N. (author), Beekman, M.C. (author), Ali, H.A.S. (author), Ferreira Marques, J.M. (author), Zachariadis, C. (author), Veen, H.M. (author), Stavenga, T. (author), Haider, S.N. (author), DiCarlo, L. (author)

We present the use of a set of airbridges to trim the frequency of microwave coplanar-waveguide (CPW) resonators post-fabrication. This method is compatible with the fabrication steps of conventional CPW airbridges and crossovers and increases device yield by allowing compensation of design and fabrication uncertainty with 100 MHz range and...

journal article 2023

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Lower-temperature fabrication of airbridges by grayscale lithography to increase yield of nanowire transmons in circuit QED quantum processors

Stavenga, T. (author), Khan, S. A. (author), Liu, Y. (author), Krogstrup, P. (author), DiCarlo, L. (author)

Quantum hardware based on circuit quantum electrodynamics makes extensive use of airbridges to suppress unwanted modes of wave propagation in coplanar-waveguide transmission lines. Airbridges also provide an interconnect enabling transmission lines to cross. Traditional airbridge fabrication produces a curved profile by reflowing resist at...

journal article 2023

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Realization of a quantum neural network using repeat-until-success circuits in a superconducting quantum processor

Vlothuizen, W.J. (author), Ferreira Marques, J.M. (author), van Straten, J. (author), Ali, H. (author), Muthusubramanian, N. (author), Zachariadis, C. (author), van Someren, J. (author), Beekman, M. (author), Haider, S.N. (author), Bruno, A. (author), Almudever, Carmen G. (author), DiCarlo, L. (author)

Artificial neural networks are becoming an integral part of digital solutions to complex problems. However, employing neural networks on quantum processors faces challenges related to the implementation of non-linear functions using quantum circuits. In this paper, we use repeat-until-success circuits enabled by real-time control-flow...

journal article 2023

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High-Fidelity Controlled- Z Gate with Maximal Intermediate Leakage Operating at the Speed Limit in a Superconducting Quantum Processor

Negîrneac, V. (author), Ali, H.A.S. (author), Muthusubramanian, N. (author), Battistel, F. (author), Sagastizabal, R.E. (author), Moreira, M. S. (author), Ferreira Marques, J.M. (author), Vlothuizen, W.J. (author), Beekman, M.C. (author), Zachariadis, C. (author), Haider, S.N. (author), Bruno, A. (author), DiCarlo, L. (author)

Simple tuneup of fast two-qubit gates is essential for the scaling of quantum processors. We introduce the sudden variant (SNZ) of the net zero scheme realizing controlled-Z (CZ) gates by flux control of transmon frequency. SNZ CZ gates realized in a multitransmon processor operate at the speed limit of transverse coupling between...

journal article 2021

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Variational preparation of finite-temperature states on a quantum computer

Sagastizabal, R.E. (author), Klaver, B. A. (author), Rol, M.A. (author), Negîrneac, V. (author), Zou, X. (author), Muthusubramanian, N. (author), Beekman, M. (author), Zachariadis, C. (author), Ostroukh, V.P. (author), Haider, S.N. (author), Bruno, A. (author), DiCarlo, L. (author)

The preparation of thermal equilibrium states is important for the simulation of condensed matter and cosmology systems using a quantum computer. We present a method to prepare such mixed states with unitary operators and demonstrate this technique experimentally using a gate-based quantum processor. Our method targets the generation of...

journal article 2021

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Leakage detection for a transmon-based surface code

Varbanov, B.M. (author), Battistel, F. (author), Tarasinski, B.M. (author), Ostroukh, V.P. (author), O’Brien, Thomas Eugene (author), DiCarlo, L. (author), Terhal, B.M. (author)

Leakage outside of the qubit computational subspace, present in many leading experimental platforms, constitutes a threatening error for quantum error correction (QEC) for qubits. We develop a leakage-detection scheme via Hidden Markov models (HMMs) for transmon-based implementations of the surface code. By performing realistic density-matrix...

journal article 2020

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Time-domain characterization and correction of on-chip distortion of control pulses in a quantum processor

Rol, M.A. (author), Ciorciaro, L.S.L. (author), Malinowski, F.K. (author), Tarasinski, B.M. (author), Sagastizabal, R.E. (author), Bultink, C.C. (author), Salathe, Y. (author), Haandbaek, N. (author), Sedivy, J. (author), DiCarlo, L. (author)

We introduce Cryoscope, a method for sampling on-chip baseband pulses used to dynamically control qubit frequency in a quantum processor. We specifically use Cryoscope to measure the step response of the dedicated flux control lines of two-junction transmon qubits in circuit QED processors with the temporal resolution of the room-temperature...

journal article 2020

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Protecting quantum entanglement from leakage and qubit errors via repetitive parity measurements

Bultink, C.C. (author), O'Brien, T. E. (author), Vollmer, R. (author), Muthusubramanian, N. (author), Beekman, M. W. (author), Rol, M.A. (author), Fu, X. (author), Tarasinski, B.M. (author), Ostroukh, V.P. (author), Varbanov, B.M. (author), Bruno, A. (author), DiCarlo, L. (author)

Protecting quantum information from errors is essential for large-scale quantum computation. Quantum error correction (QEC) encodes information in entangled states of many qubits and performs parity measurements to identify errors without destroying the encoded information. However, traditional QEC cannot handle leakage from the qubit...

journal article 2020

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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

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Fast, High-Fidelity Conditional-Phase Gate Exploiting Leakage Interference in Weakly Anharmonic Superconducting Qubits

Rol, M.A. (author), Battistel, F. (author), Malinowski, F.K. (author), Bultink, C.C. (author), Tarasinski, B.M. (author), Vollmer, R. (author), Haider, S.N. (author), Muthusubramanian, N. (author), Bruno, A. (author), Terhal, B.M. (author), DiCarlo, L. (author)

Conditional-phase (cz) gates in transmons can be realized by flux pulsing computational states towards resonance with noncomputational ones. We present a 40 ns cz gate based on a bipolar flux pulse suppressing leakage (0.1%) by interference and approaching the speed limit set by exchange coupling. This pulse harnesses a built-in echo to...

journal article 2019

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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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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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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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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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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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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