arXiv subjects

Edwin Acuna

Publications and source records attributed to Edwin Acuna.

7 recordsLinked to original sources

arXiv2026

A digitally controlled silicon quantum processing unit

Commercially-relevant quantum computers will require large numbers of high-performing qubits that can be manufactured, integrated, and controlled at scale. Silicon exchange-only (EO) qubits are a strong candidate modality due to their control-signal simplicity and compatibility with advanced semiconductor manufacturing, but questions remain around the achievability of sufficiently low noise and a scalable control and wiring solution. Here we introduce a quantum processing unit composed of a custom-designed cryogenic CMOS controller, a novel high-density superconducting ribbon cable, and a low-noise EO qubit device. The quantum chip features a three-rail array of 54 exchange-coupled quantum dots, configurable to host up to 18 EO qubits. We integrate and use these components to demonstrate qubit performance for both single-qubit and entangling operations that advances the EO state of the art by an order of magnitude. We further validate this system by implementing a distance-5 repetition code and a quantum error detecting code then make detailed comparisons with simulations. Our approach facilitates a utility-scale quantum computer with manageable operational and capital requirements.

quant-ph↗

arXiv2026

Leakage-protected idle operation of a triangular exchange-only spin qubit

We characterize the coherence of a triangular exchange-only (EO) spin qubit operated at a leakage-protected idle (LPI) point. The triangular geometry enables independent control of all three pairwise exchange interactions, and the LPI condition occurs when these couplings are turned on simultaneously and tuned to equal strength. In this configuration, the exchange interaction induces an energy gap $E_g = 3J/2$ that suppresses leakage from the computational subspace while leaving the qubit state unaffected. We develop procedures to calibrate the LPI point and measure $E_g$, and use these to characterize the qubit dephasing time over a broad range of gap energies. While operating with large always-on exchange couplings exposes the qubit to charge noise, we find that $\tilde{T}_2^*$ still exceeds that of conventional exchange-only spin qubits for $E_g/h < 60$ MHz. The precise control of simultaneous, all-to-all connected exchange demonstrated here presents a natural path towards improving the performance of EO qubits and also enables novel qubit encodings.

quant-ph↗

arXiv2025

Demonstration of an always-on exchange-only spin qubit

In conventional exchange-only (EO) spin qubit demonstrations, quantum gates have been implemented using sequences of individually pulsed pairwise exchange interactions with only one exchange coupling active at a time. Alternatively, multiple non-commuting exchange interactions can be pulsed simultaneously, reducing circuit depths and providing protection against leakage. We demonstrate high-fidelity quantum control of an always-on exchange-only (AEON) qubit, operated using simultaneous exchange pulses in a triangular quantum dot (QD) array. We use blind randomized benchmarking to characterize the performance of the full AEON single-qubit Clifford gate set, achieving an average Clifford gate fidelity $F_{\rm C1}$ = 99.86%. Extensions of this work may enable more efficient EO two-qubit entangling gates as well as the implementation of native $i$-Toffoli gates in Loss-DiVincenzo single-spin qubits.

quant-ph↗

arXiv2025

Two-dimensional Si spin qubit arrays with multilevel interconnects

The promise of quantum computation is contingent upon physical qubits with both low gate error rate and broad scalability. Silicon-based spins are a leading qubit platform, but demonstrations to date have not utilized fabrication processes capable of extending arrays in two dimensions while maintaining complete control of individual spins. Here, we implement an interconnect process, common in semiconductor manufacturing, with multiple back-end-of-line layers to show an extendable two-dimensional array of spins with fully controllable nearest-neighbor exchange interactions. In a device using three interconnect layers, we encode exchange-only qubits and achieve average single-qubit gate fidelities consistent with single-layer devices, including fidelities greater than 99.9%, as measured by blind randomized benchmarking. Moreover, with spin connectivity in two dimensions, we show that both linear and right-angle exchange-only qubits with high performance can be formed, enabling qubit array reconfigurability in the presence of defects. This extendable device platform demonstrates that industrial manufacturing techniques can be leveraged for scalable spin qubit technologies.

quant-ph↗

arXiv2024

Coherent control of a triangular exchange-only spin qubit

We demonstrate coherent control of a three-electron exchange-only spin qubit with the quantum dots arranged in a close-packed triangular geometry. The device is tuned to confine one electron in each quantum dot, as evidenced by pairwise charge stability diagrams. Time-domain control of the exchange coupling is demonstrated and qubit performance is characterized using blind randomized benchmarking, with an average single-qubit gate fidelity F = 99.84%. The compact triangular device geometry can be readily scaled to larger two-dimensional quantum dot arrays with high connectivity.

cond-mat.mes-hall↗

arXiv2021

A flexible design platform for Si/SiGe exchange-only qubits with low disorder

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 non-trivial 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.

cond-mat.mes-hall↗

arXiv2020

Detuning Axis Pulsed Spectroscopy of Valley-Orbital States in Si/SiGe Quantum Dots

Silicon quantum dot qubits must contend with low-lying valley excited states which are sensitive functions of the quantum well heterostructure and disorder; quantifying and maximizing the energies of these states are critical to improving device performance. We describe a spectroscopic method for probing excited states in isolated Si/SiGe double quantum dots using standard baseband pulsing techniques, easing the extraction of energy spectra in multiple-dot devices. We use this method to measure dozens of valley excited state energies spanning multiple wafers, quantum dots, and orbital states, crucial for evaluating the dependence of valley splitting on quantum well width and other epitaxial conditions. Our results suggest that narrower wells can be beneficial for improving valley splittings, but this effect can be confounded by variations in growth and fabrication conditions. These results underscore the importance of valley splitting measurements for guiding the development of Si qubits.

cond-mat.mes-hall↗