Improved Stability of Electron Spins in Qubits
September 8, 2015 | University of BaselEstimated reading time: 2 minutes
Calculation with electron spins in a quantum computer assumes that the spin states last for a sufficient period of time. Physicists at the University of Basel and the Swiss Nanoscience Institute have now demonstrated that electron exchange in quantum dots fundamentally limits the stability of this information. Control of this exchange process paves the way for further progress in the coherence of the fragile quantum states. The report from the Basel-based researchers appears in the scientific journal Physical Review Letters.
The basic idea of a quantum computer is to replace the ones and zeros used in today’s bits with quantum states, or qubits. Qubits are units of information that not only assume the values zero and one, but in which zero and one are possible at the same time, and in any chosen combination, in the form of a quantum superposition. Qubits can, for example, be implemented using the spins of individual electrons held in nanoscale structures made of semiconducting material, known as quantum dots. By exploiting quantum-mechanical principles such as superposition, a quantum computer can achieve enormous processing speeds – but only if the electron spins persist for long enough.
In recent years, it has been possible to extend this so-called coherence time to over a millisecond, thanks to the successful reduction of interference caused by nuclear spins. Thus, the search for other factors that affect the stability of the electron spins increased in importance.
Discovery of electron exchange
Physicists at the University of Basel and the Swiss Nanoscience Institute have now established that qubits’ coherence is limited by a process in which individual electrons are exchanged between a quantum dot and an external reservoir. The reservoir represents a type of electrode that is in contact with the quantum dot and is required for the measurements.
The researchers, led by Professor Dominik Zumbühl, observed that thermal excitation prompts an electron to jump from the quantum dot into the reservoir, and that shortly thereafter an electron jumps from the reservoir into the quantum dot.
This exchange creates a short-lived charge state, which the researchers in Basel have now been able to demonstrate for the first time with a charge sensor. The exchange process also leads to a randomizing of the electron spins, through which quantum information is lost.
Fundamental process for coherence
Based on the experimental observations, the researchers were able to significantly extend the existing theoretical description of double quantum dots, which can contain two electrons. They also succeeded in influencing the intensity of the temperature-dependent exchange process by cooling the electrons down to 60 millikelvins. At the same time, the process was slowed and the stability of the spins prolonged by changing the voltages at the entrances, or gates, to the quantum dot.
An understanding and control of this exchange process, which is fundamental to quantum dots, paves the way for further progress in qubit coherence. At the same time, it opens the way to a quick generation of desired spin states in quantum dots.
Implementation of a theoretical concept with Basel roots
This approach, whereby quantum dots in semiconductors are exploited in order to use the spin of an individual electron as a qubit, can be traced back to Prof. Daniel Loss of the University of Basel and the American physicist David DiVincenzo. Their concept, which they originally presented in 1998, has the potential to allow the creation of quantum computers with a large number of connected spin qubits. The current study was carried out in collaboration with researchers from the University of St Andrews (GB) and the University of California, Santa Barbara (US).
Suggested Items
Koh Young Showcases Award-winning Inspection Solutions at SMTconnect with SmartRep in Hall 4A.225
04/25/2024 | Koh Young TechnologyKoh Young Technology, the industry leader in True 3D measurement-based inspection solutions, will showcase an array of award-winning inspection and measurement solutions at SMTconnect alongside its sales partner, SmartRep, in booth 4A.225 at NürnbergMesse from June 11-13, 2023. The following offers a glimpse into what Koh Young will present at the tradeshow:
Real Time with… IPC APEX EXPO 2024: Plasmatreat: Innovative Surface Preparation Solutions
04/25/2024 | Real Time with...IPC APEX EXPOIn this interview, Editor Nolan Johnson speaks with Hardev Grewal, CEO and president of Plasmatreat, a developer of atmospheric plasma solutions. Plasmatreat uses clean compressed air and electricity to create plasma, offering environmentally friendly methods for surface preparation. Their technology measures plasma density for process optimization and can remove organic micro-contamination. Nolan and Hardev also discuss REDOX-Tool, a new technology for removing metal oxides.
KYZEN to Promote Pair of Stencil Cleaning Chemistries at SMTA Ciudad Jaurez Expo & Tech Forum
04/25/2024 | KYZEN'KYZEN, the global leader in innovative environmentally friendly cleaning chemistries, will exhibit at the SMTA Ciudad Juarez Expo & Tech Forum, scheduled to take place Thursday, May 9, 2024 at the Injectronic Convention Center in Ciudad Jaurez, Chihuahua, Mexico. During the event the KYZEN Clean Team will focus on understencil cleaning products KYZEN E5631J and CYBERSOLV C8882.
Cadence, TSMC Collaborate on Wide-Ranging Innovations to Transform System and Semiconductor Design
04/25/2024 | Cadence Design SystemsCadence Design Systems, Inc. and TSMC have extended their longstanding collaboration by announcing a broad range of innovative technology advancements to accelerate design, including developments ranging from 3D-IC and advanced process nodes to design IP and photonics.
Listen Up! The Intricacies of PCB Drilling Detailed in New Podcast Episode
04/25/2024 | I-Connect007In episode 5 of the podcast series, On the Line With: Designing for Reality, Nolan Johnson and Matt Stevenson continue down the manufacturing process, this time focusing on the post-lamination drilling process for PCBs. Matt and Nolan delve into the intricacies of the PCB drilling process, highlighting the importance of hole quality, drill parameters, and design optimization to ensure smooth manufacturing. The conversation covers topics such as drill bit sizes, aspect ratios, vias, challenges in drilling, and ways to enhance efficiency in the drilling department.