A Flexible Design Platform for Si/SiGe Exchange-Only Qubits with Low Disorder

Abstract

Spin-based silicon quantum dots are an attractive qubit technology for quantum information processing with respect to coherence time, control, and engineering. Here we present an exchange-only Si qubit device platform that combines the throughput of CMOS-like wafer processing with the versatility of direct-write lithography. The technology, which we coin “SLEDGE”, features dot-shaped gates that are patterned simultaneously on one topographical plane and subsequently connected by vias to interconnect metal lines. The process design enables nontrivial layouts as well as flexibility in gate dimensions, material selection, and additional device features such as for rf qubit control. We show that the SLEDGE process has reduced electrostatic disorder with respect to traditional overlapping gate devices with lift-off metallization, and we present spin coherent exchange oscillations and single qubit blind randomized benchmarking data.

Two-qubit silicon quantum processor with operation fidelity exceeding 99%

“…These experiments demonstrate two-qubit gates with silicon spin qubits at speeds exceeding trapped ions ( 33 ) and fidelities comparable with superconducting qubits ( 14 , 15 ). Given recent advances in quantum dot fabrication ( 16 , 34 ), spin qubits are poised to scale-up to larger multiqubit quantum processors.…”

Universal logic with encoded spin qubits in silicon

“…At fields > 3 mT, error increases again due to a combination of spin-orbit effects and Meissner screening effects from superconducting parts of the gate-stack (see Appendix C). This effect is stronger in earlier devices employing aluminum metal [20], but is much weaker in the present device due to the non-or weakly-superconducting TiN gates used in the SLEDGE process [18]. From this plot we may infer that the IRB shown in Fig.…”

“…This type of noise induces error only during active exchange pulsing, since nearest-neighbor tunnel coupling is suppressed when the associated spins are idling. This idle-error-suppression results from the exponential scaling of the spin-spin exchange interaction with applied barrier potentials in general, and in particular from the large on-off ratios that are available with our tightly-confining SLEDGE design [18]. As shown in Fig.…”

“…Though EO control was proposed over twenty years ago [16], experimental demonstration of encoded entangling operations has waited for the availability of fullyfunctional six-dot devices. Three recent advances enabled the result we report on here: the Single Layer Etch-Defined Gate Electrode (SLEDGE) process [18] for making high-yielding devices, the use of narrow Si/Si 0.3 Ge 0.7 quantum wells to increase the probability that dots have sufficiently large valley energy for measurement and initialization [9], and improved control software to manage the complexity of these larger quantum manipulations [1]. Using these, we demonstrate an average 2-qubit Clifford fidelity of 97.1 ± 0.2% and the FW controlled-NOT gate [17,19] (FW-CNOT) with 96.3 ± 0.7% fidelity, both limited by well-understood sources of magnetic noise [20], and an encoded SWAP operation with 99.3 ± 0.5% fidelity.…”

“…We also demonstrate a "leakage controlled" controlled-Z (LCCZ) gate, requiring 45 exchange pulses, with 93.8 ± 0.7% fidelity. The LCCZ improves on FW gates by preventing occupation of unencoded "leaked" spin states from spreading, a feature which may prove critical to FT. Our SLEDGE-based device [18] is composed of six quantum dots arranged in a line, corresponding to two three-spin EO qubits. Electrons are vertically confined in a 5-nm-thick silicon well surrounded by isotopically natural Si 0.3 Ge 0.7 barriers.…”