Quantum process tomography of a universal entangling gate implemented with Josephson phase qubits

By R. Bialczak, M. Ansmann, M. Hofheinz, E. Lucero, Matthew Neeley, A. O'Connell, D. Sank, Haohua Wang, J. Wenner, Matthias Steffen and 9 more. 2009

234 citations recorded by the source corpus.

Quantum process tomography provides a means of benchmarking the components and algorithms of a quantum computer in a quantitative fashion, independent of the particular architecture used. Such a procedure has now been demonstrated for a universal entangling gate in a solid-state system. Quantum gates must perform reliably when operating on standard input basis states and on complex superpositions thereof. Experiments using superconducting qubits have validated truth tables for particular implementations of, for example, the controlled-NOT gate1,2, but have not fully characterized gate operation for arbitrary superpositions of input states. Here we demonstrate the use of quantum process tomography3,4 (QPT) to fully characterize the performance of a universal entangling gate between two superconducting qubits. Process tomography permits complete gate analysis, but requires precise preparation of arbitrary input states, control over the subsequent qubit interaction and ideally simultaneous single-shot measurement of output states. In recent work, it has been proposed to use QPT to probe noise properties5 and time dynamics6 of qubit systems and to apply techniques from control theory to create scalable qubit benchmarking protocols7,8. We use QPT to measure the fidelity and noise properties5 of an entangling gate. In addition to demonstrating a promising fidelity, our entangling gate has an on-to-off ratio of 300, a level of adjustable coupling that will become a requirement for future high-fidelity devices. This is the first solid-state demonstration of QPT in a two-qubit system, as QPT has previously been demonstrated only with single solid-state qubits9,10,11.

Subfields: Artificial Intelligence, Atomic and Molecular Physics, and Optics

View Paper: https://www.semanticscholar.org/paper/88b0110137b4d462051310d8b31ac747b201ebc4

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In Atomic and Molecular Physics, and Optics

Citations in the corpus

Universal Gate for Fixed-Frequency Qubits via a Tunable Bus (2016, unknown): “In the first approach the qubit frequencies are tunable and interactions are controlled by dynamically tuning pairs of qubits into and out of specific resonance conditions [3, 4].”
Tunable Coupling Scheme for Implementing High-Fidelity Two-Qubit Gates (2018, methodology): “Second, the gate infidelity (the error per gate) due to energy relaxation follows = τ/T1 (We use 16 linearly independent input states when performing process tomography [39], and there is a prefactor difference from that estimated in randomized benchmarking [40]).”
Circuit quantum electrodynamics (2020, background): “The most straightforward way is to tune the qubits in resonance to perform a two-qubit gate, and to strongly detune them to stop the coherent exchange induced by Ĥ ′ (Bialczak et al., 2010; Blais et al., 2003; Dewes et al., 2012).”
Efficient Variational Quantum Simulator Incorporating Active Error Minimization (2016, methodology): “Therefore, quantum operations need to be benchmarked, e.g. using quantum process tomography [55, 56], before the quantum coprocessor is used, and the nature of the machine noise should not vary signiﬁcantly during the simulation.”
Atomic physics and quantum optics using superconducting circuits (2011, methodology): “Also, quantum process tomography was experimentally implemented on single [65] and two [66] phase qubits.”