2022 New's Items

Bidirectional phonon emission in two-dimensional heterostructures triggered by ultrafast charge transfer

Sood A
Raja A
Neaton JB
2022

Photoinduced charge transfer in van der Waals heterostructures occurs on the 100 fs timescale despite weak interlayer coupling and momentum mismatch. However, little is understood about the microscopic mechanism behind this ultrafast process and the role of the lattice in mediating it. Here, using femtosecond electron diffraction, we directly visualize lattice dynamics in photoexcited heterostructures of WSe2/WS2 monolayers. Following the selective excitation of WSe2, we measure the concurrent heating of both WSe2 and WS2 on...

Ting Xu announced as a laureate for work in programmable plastic degradation through Enzymes

November 14, 2022
UC Berkeley, College of Chemistry

The Falling Walls Science Summit brings together important researchers and thinkers of our time to discuss breakthroughs with global leaders in science, politics, business, and the media. Prof. Xu was announced as a laureate for work in programmable plastic degradation through Enzymes.

https://chemistry.berkeley.edu/news/professor-ting-xu-honored-falling-walls-scie…

Leveraging randomized compiling for the quantum imaginary-time-evolution algorithm

Ville JL ......
Iancu C
Santiago DI
Siddiqi I
2022

Recent progress in noisy intermediate-scale quantum (NISQ) hardware shows that quantum devices may be able to tackle complex problems even without error correction. However, coherent errors due to the increased complexity of these devices is an outstanding issue. They can accumulate through a circuit, making their impact on algorithms hard to predict and mitigate. Iterative algorithms like quantum imaginary time evolution are susceptible to these errors. This article presents the combination of both noise tailoring using randomized compiling and error mitigation with purification. We...

Programmable Heisenberg interactions between Floquet qubits

Nguyen LB .......
Jordan AN
Santiago DI
Siddiqi I
2022

The fundamental trade-off between robustness and tunability is a central challenge in the pursuit of quantum simulation and fault-tolerant quantum computation. In particular, many emerging quantum architectures are designed to achieve high coherence at the expense of having fixed spectra and consequently limited types of controllable interactions. Here, by adiabatically transforming fixed-frequency superconducting circuits into modifiable Floquet qubits, we demonstrate an XXZ Heisenberg interaction with fully adjustable anisotropy. This interaction model is on one hand the basis for...

Benchmarking quantum logic operations for achieving fault tolerance

Hashim A .......
Kreikebaum JM
Santiago DI
Siddiqi I
2022

Contemporary methods for benchmarking noisy quantum processors typically measure average error rates or process infidelities. However, thresholds for fault-tolerant quantum error correction are given in terms of worst-case error rates -- defined via the diamond norm -- which can differ from average error rates by orders of magnitude. One method for resolving this discrepancy is to randomize the physical implementation of quantum gates, using techniques like randomized compiling (RC). In this work, we use gate set tomography to perform precision characterization of a set of two-qubit...

Demonstrating scalable randomized benchmarking of universal gate sets

Hines J .........
Siddiqi I
Whaley B
Proctor T
2022

Randomized benchmarking (RB) protocols are the most widely used methods for assessing the performance of quantum gates. However, the existing RB methods either do not scale to many qubits or cannot benchmark a universal gate set. Here, we introduce and demonstrate a technique for scalable RB of many universal and continuously parameterized gate sets, using a class of circuits called randomized mirror circuits. Our technique can be applied to a gate set containing an entangling Clifford gate and the set of arbitrary single-qubit gates, as well as gate sets containing controlled...

High-fidelity qutrit entangling gates for superconducting circuits

Goss N ........
Santiago DI
Wallman JJ
Siddiqi I
2022

Ternary quantum information processing in superconducting devices poses a promising alternative to its more popular binary counterpart through larger, more connected computational spaces and proposed advantages in quantum simulation and error correction. Although generally operated as qubits, transmons have readily addressable higher levels, making them natural candidates for operation as quantum three-level systems (qutrits). Recent works in transmon devices have realized high fidelity single qutrit operation. Nonetheless, effectively engineering a high-fidelity two-qutrit...

Blueprint for a High-Performance Fluxonium Quantum Processor

Nguyen LB .......
Puri KN
Santiago DI
Siddiqi I
2022

Transforming stand-alone qubits into a functional, general-purpose quantum processing unit requires an architecture where many-body quantum entanglement can be generated and controlled in a coherent, modular, and measurable fashion. Electronic circuits promise a well-developed pathway for large-scale integration once a mature library of quantum-compatible elements have been developed. In the domain of superconducting circuits, fluxonium has recently emerged as a promising qubit due to its high-coherence and large anharmonicity, yet its scalability has not been systematically explored...

Optimizing frequency allocation for fixed-frequency superconducting quantum processors

Morvan A
Chen L
Larson JM
Santiago DI
Siddiqi I
2022

Fixed-frequency superconducting quantum processors are one of the most mature quantum computing architectures with high-coherence qubits and simple controls. However, high-fidelity multiqubit gates pose tight requirements on individual qubit frequencies in these processors, and these constraints are difficult to satisfy when constructing larger processors due to the large dispersion in the fabrication of Josephson junctions. In this paper, we propose a mixed-integer-programming-based optimization approach that determines qubit frequencies to maximize the fabrication yield of quantum...

Optimized SWAP networks with equivalent circuit averaging for QAOA

Hashim A
Rines R
Omole V
Naik RK
Kreikebaum JM
Santiago DI
Chong FT
Siddiqi I
Gokhale P
2022

The SWAP network is a qubit routing sequence that can be used to efficiently execute the Quantum Approximate Optimization Algorithm (QAOA). Even with a minimally connected topology on an n-qubit processor, this routing sequence enables O(n2) operations to execute in ...