Suppression of Qubit Crosstalk in a Tunable Coupling Superconducting Circuit

Abstract

Parasitic crosstalk in superconducting quantum devices is a leading limitation for quantum gates. We demonstrate the suppression of static ZZ crosstalk in a two-qubit, two-coupler superconducting circuit, where the frequency of a tunable coupler can be adjusted such that the ZZ interaction from each coupler destructively interfere. We verify the crosstalk elimination with simultaneous randomized benchmarking, and use a parametrically activated iSWAP interaction to achieve a Bell state preparation fidelity of 98.5% and a √ iSWAP gate fidelity of 94.8% obtained via quantum process tomography.PACS numbers: 03.67. Lx, 42.50.Dv, 85.25.Cp Circuit quantum electrodynamics (cQED) [1], which uses superconducting circuits as its building blocks, has become a promising candidate and testbed for implementing quantum computation. Remarkable research progress has been made in integrating more qubits, resonators and other circuit elements in order to build increasingly computationally powerful devices [2,3]. As the number of circuit elements and control signals scales up in a cQED device, undesirable responses to external controls and unwanted interactions between subsystems lead to crosstalk that must be carefully calibrated and eliminated to ensure optimal device performance [4,5]. The trade-off between strong qubit-qubit interaction (for fast gates) and low crosstalk poses constraints on the device design and pulse schemes [6,7]. In a cQED system where multiple transmon qubits [8] are coupled via bus cavities [9], the couplings between their higher energy levels give rise to cross-Kerr interactions that can be described by ζa † i a i a † j a j [10], where a (a † ) is the annihilation (creation) operator for the qubit modes, and ζ corresponds to the frequency shift of qubit i depending on the state of qubit j (and vice versa). This type of static ZZ crosstalk causes dephasing in the qubits and degrades device performance if ζ is comparable to the qubit decoherence rate. In particular, it limits the fidelity of XX -type parity measurements in several quantum error correction schemes [11] and the lifetime of logical qubits containing XX -type stabilizers [4]. Theoretical and experimental studies have shown that ZZ crosstalk has become the limiting factor for gate fidelity as qubit coherence times keep improving in state-of-theart devices [12].In this work, we utilize quantum interference in a tunable coupling device to demonstrate the suppression of static ZZ crosstalk. By introducing a tunable coupler in addition to the bus cavity, shown schematically in Fig. 1(a), ζ can be tuned to zero and that an efficient two-qubit gate can be implemented with ζ = 0. Nulling * These authors contributed equally to this work. † aahouck@princeton.edu of the always-on ZZ interaction is verified by simultaneous randomized benchmarking (RB). Parametrically activated entangling gates, which have been widely employed in superconducting circuits [13][14][15][16][17][18], can be easily implemented in this architecture. While modulating the coupler...

Realizing a deterministic source of multipartite-entangled photonic qubits

“…The coupling between the auxiliary system and the emitter is mediated by two parallel channels, one of which is tunable via the magnetic flux applied to a superconducting quantum interference device loop. This specific coupler arrangement (green) allows us to interferometrically cancel the static coupling and protect the auxiliary transmon from Purcell decay into the transmission line while enabling fast decay of the emitter 17 , 18 .

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Benchmarking the noise sensitivity of different parametric two-qubit gates in a single superconducting quantum computing platform

“…Synchronization of such coherent Rabi oscillations into leakage channels can minimize leakage errors [54]. On the device end, strategies to mitigate always-on ZZ-type interactions [36,37] need to be devised that can be readily employed in scalable architectures.…”

“…phase errors caused by coupler-induced frequency drifts of the qubits, (D) drive-induced dispersive shifts during the gate caused by the coupling between qubits and the modulated TC, (E) static ZZ-type errors caused by the interaction between |11 and |20 states [36,37], and (F) intrinsic dissipation and decoherence (T 1 and T 2 ).…”

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“…Steady progress in improving gate fidelities for superconducting qubits over the last two decades has enabled key demonstrations of quantum algorithms 1 – 3 , quantum error correction 4 – 6 , and quantum supremacy 7 . These demonstrations have relied on either improving coherence through microwave engineering to avoid losses associated with surfaces and interfaces 8 – 10 and to minimize the effects of thermal noise and quasiparticles 11 – 14 , or by realizing fast gates using tunable coupling 15 , 16 . By contrast, little progress has been made in addressing the microscopic source of loss and noise in the constituent materials.…”