Reducing Noise in Silicon Quantum Dots Boosts Calculation Precision
March 26, 2018 | RIKENEstimated reading time: 2 minutes
Using ultrapure crystals of silicon and micromagnets, RIKEN researchers have demonstrated enhanced electrical control over the directions in which electron spins point inside tiny boxes in silicon called quantum dots. This approach, which operates quantum logic gates with 99.9% precision, offers an attractive pathway for manufacturing fault-tolerant quantum computers on a large scale.
Quantum bits, or ‘qubits’, exploit quantum superposition states to generate far higher computational powers than conventional semiconductor circuits. Electron spins are leading candidates for such qubits, which can be implemented in structures similar to today’s computing devices.
To perform practical numbers of computing operations, these spin qubits need to maintain the superposition of ‘up’ and ‘down’ spin orientations for extended times—a property known as coherence. Unfortunately, these spin states are highly sensitive to magnetic noise from surrounding atoms, such as those on silicon chips.
“In this kind of semiconductor nanodevice, a single electron is typically coupled to thousands of other nuclei, which can degrade the spin coherence,” explains Jun Yoneda of the RIKEN Center for Emergent Matter Science. “Even though 95 per cent of the nuclei in silicon don’t interfere, the remaining nuclear spins are the dominant source of noise in our qubits.”
Yoneda and colleagues in Seigo Tarucha’s group are seeking to improve qubit circuit performance by mitigating magnetic contamination. One way they are achieving this is by ensuring atoms inside their silicon chips are all the same isotope—that is, they all have the same number of neutrons in their nuclei. This procedure reduces magnetic noise sources to less than 0.08 per cent. However, orienting spins in ultrapure samples is time consuming because the coherent states are so isolated from the electromagnetic environment.
To direct spin more effectively, the researchers fabricated quantum dots on isotopically pure silicon and then used tiny micromagnets to introduce magnetic fields in specific lateral and perpendicular directions across the dot. By applying a series of phase-corrected electrical pulses along the magnetic fields, they coupled the control hardware to a single electron spin and switched its orientation at rates of up to 30 million times per second. Experiments with qubit logic gates revealed the new spin–electric coupling procedure reduced quantum computing error rates to record low levels.
The residual noise in the system came from random fluctuations in charge—a finding that contradicts previous observations about spin coherence. “This is surprising because a single electron spin is much more sensitive to magnetic environments than electric ones,” says Yoneda. “But it comes from having enhanced coherence and controllability, and it points to future improvements by using established routines to reduce charge noise.”
Suggested Items
Connect the Dots: Best Practices for Prototyping
09/21/2023 | Matt Stevenson -- Column: Connect the DotsPCB prototyping is a critical juncture during an electronic device’s journey from concept to reality. Regardless of a project’s complexity, the process of transforming a design into a working board is often enlightening in terms of how a design can be improved before a PCB is ready for full production.
The Drive Toward UHDI and Substrates
09/20/2023 | I-Connect007 Editorial TeamPanasonic’s Darren Hitchcock spoke with the I-Connect007 Editorial Team on the complexities of moving toward ultra HDI manufacturing. As we learn in this conversation, the number of shifting constraints relative to traditional PCB fabrication is quite large and can sometimes conflict with each other.
Asia/Pacific AI Spending Surge to Reach a Projected $78 Billion by 2027
09/19/2023 | IDCAsia/Pacific spending on Artificial Intelligence (AI) ), including software, services, and hardware for AI-centric systems will grow to $78.4 billion in 2027, according to International Data Corporation's latest Worldwide Artificial Intelligence Spending Guide.
Intel to Sell Minority Stake in IMS Nanofabrication Business to TSMC
09/13/2023 | IntelIntel Corporation announced that it has agreed to sell an approximately 10% stake in the IMS Nanofabrication business to TSMC. TSMC’s investment values IMS at approximately $4.3 billion, consistent with the valuation of the recent stake sale to Bain Capital Special Situations.
RAF Invests in BAE Systems’ Most Advanced Fighter Pilot Helmet
09/13/2023 | BAE SystemsThe UK Ministry of Defence (MOD) has awarded BAE Systems a contract to develop its Striker II Helmet Mounted Display (HMD) for the Royal Air Force (RAF) Typhoon fleet. The contract, valued at £40m, will create and sustain more than 200 highly-skilled jobs at BAE Systems’ sites in Kent and Lancashire working directly on the Striker II programme. In total, the Typhoon programme sustains more than 20,800 jobs across the UK.