Superconducting quantum processors enable precise insights into quantum transport

Los Angeles CA (SPX) Dec 06, 2024
Researchers from Singapore and China have achieved a significant milestone by leveraging a superconducting quantum processor to explore quantum transport with unparalleled precision.

Quantum transport, which involves the flow of particles, magnetization, energy, or information through a quantum system, holds potential to drive advancements in nanoelectronics and thermal management technologies.

"This represents, practically, a new paradigm of doing quantum transport experiments," explained Centre for Quantum Technologies (CQT) Fellow Dario Poletti. Poletti, along with Professors Haohua Wang from Zhejiang University (ZJU) and Jie Hao from the Chinese Academy of Sciences (CAS), co-authored the study published in *Nature Communications* on November 22, 2024. He added, "We can now access information that we could not before with other previous implementations of quantum transport."

Theoretical and Experimental Collaboration

Poletti, who is also an Associate Professor at Singapore University of Technology and Design (SUTD), worked with Dr. Xiansong Xu and Dr. Chu Guo to develop theoretical models for quantum transport. These models, conceived during their doctoral studies at SUTD, were tested through collaborations with experimental teams from ZJU and CAS. The experimental efforts utilized ZJU's 31-qubit quantum processor to investigate spin and particle currents between qubits.

"The work also shows the usefulness of quantum simulation in the NISQ era," noted Pengfei Zhang, a Postdoctoral Fellow at ZJU. NISQ, or noisy intermediate-scale quantum devices, represents the current phase of quantum hardware development. Pengfei co-authored the study alongside Yu Gao, a ZJU PhD student, and Xiansong.

Key Findings on Quantum Transport

The experiments focused on quantum transport between two groups of qubits with varying magnetization. One group was initialized entirely in a spin-down state, while the other contained an equal mix of spin-up and spin-down states, resulting in zero magnetization. These groups, or "baths," were connected by a weak link between qubits from each bath.

The research team studied the transport dynamics, observing how the initial configurations and system size influenced the scale and steadiness of particle currents. By preparing 60 distinct initial states for systems containing 14, 17, and 31 qubits, the researchers measured the resulting current after 200 nanoseconds. They found that the current converged to a consistent value as system size increased.

"This is sometimes called 'typicality,'" said Dario. "All that matters is the average spin polarization, a macroscopic quantity, not the details of the individual qubits or how they are prepared."

Steady-State Dynamics

Temporal fluctuations of spin flow between the baths were also measured. Over 60,000 measurements, researchers tracked these fluctuations at five-nanosecond intervals between 100 and 1,000 nanoseconds. They observed a significant reduction in fluctuations relative to the main signal as the system grew, signaling the emergence of macroscopic physics.

Pengfei explained, "It became challenging to fine-tune the control parameters and precisely measure the tiny temporal fluctuation of particle current for a large system, but we overcame it by developing a calibration protocol and an error mitigation method."

The team plans to extend their work, exploring more complex quantum transport scenarios. Their continued collaboration aims to deepen understanding and applications of quantum transport in diverse contexts.

Research Report:Emergence of steady quantum transport in a superconducting processor