Diabatic Gates for Frequency-Tunable Superconducting Qubits

Abstract

We demonstrate diabatic two-qubit gates with Pauli error rates down to 4.3(2) · 10 −3 in as fast as 18 ns using frequency-tunable superconducting qubits. This is achieved by synchronizing the entangling parameters with minima in the leakage channel. The synchronization shows a landscape in gate parameter space that agrees with model predictions and facilitates robust tune-up. We test both iSWAP-like and CPHASE gates with cross-entropy benchmarking. The presented approach can be extended to multibody operations as well.

Leakage detection for a transmon-based surface code

“…Recent advances in qubit numbers [1][2][3][4] , as well as operational [5][6][7][8][9][10][11][12][13] , and measurement [14][15][16] fidelities have enabled leading quantum computing platforms, such as superconducting and trapped-ion processors, to target demonstrations of quantum error correction (QEC) [17][18][19][20][21][22][23] and quantum advantage 2,[24][25][26] . In particular, twodimensional stabilizer codes, such as the surface code, are a promising approach 23,27 towards achieving quantum fault tolerance and, ultimately, large-scale quantum computation 28 .…”

“…In practice, many qubits such as weakly-anharmonic transmons, as well as hyperfine-level trapped ions, are many-level systems which function as qubits by restricting the interactions with the other excited states. Due to imprecise control 12,29,30 or the explicit use of non-computational states for operations 5,6,9,11,[31][32][33][34][35] , there exists a finite probability for information to leak from the computational subspace. Thus, leakage constitutes an error that falls outside of the domain of the qubit stabilizer formalism.…”

“…Furthermore, leakage can last over many QEC cycles, despite having a finite duration set by the relaxation time 36 . Hence, leakage represents a menacing error source in the context of quantum error correction 17,[36][37][38][39][40][41][42][43] , despite leakage probabilities per operation being smaller than readout, control or decoherence error probabilities 6,8,9,44 .…”

Realisation of high-fidelity nonadiabatic CZ gates with superconducting qubits

“…Motivated by the quest for quantum error correction and expanding the set of realisable circuits, 1,2 there has been a great effort to improve the design of entangling gates, [1][2][3][4][5][6][7][8][9][10][11] and by now there is a rich array of design choices in a variety of quantum computing modalities, including superconducting quantum circuits, 12 trapped ions, 13 quantum dots 14 and NV diamonds. 15,16 Notable designs for entangling gates in superconducting circuits, include fast adiabatic gates, 17 frequency modulation, 11,18 cross resonance 19,20 and resonator-induced phase, 21,22 which effect the gates using longitudinal (first two) or transverse (last two) control of the qubits.…”

Demonstrating a Continuous Set of Two-qubit Gates for Near-term Quantum Algorithms

“…Conclusions.-We have implemented continuous iSWAP-like and CPHASE gate families with average Pauli error rates of 1.2 × 10 −3 and 1.9 × 10 −3 , respectively. These fast (13-15 ns) gates take advantage of the strong, tunable, qubit-qubit coupling offered by our gmon transmon qubit architecture, achieving error rates more than a factor of 2 lower than the best previously reported twoqubit gates for superconducting qubits [32]. Additionally, we have combined these two gate sets to demonstrate a complete implementation of the two-qubit fSim gate set with an average Pauli error of 3.83 × 10 −3 per gate.…”