Intricately-shaped pulses of light pave a speedway for the accelerated dynamics of quantum particles, enabling faster switching of a quantum bit. Credit: Image courtesy Peter Allen
Speeding up control over quantum states in atomic and nanoscale systems could lead to leaps for the emerging field of quantum technology. An international collaboration between physicists recently demonstrated a new framework for faster control of a quantum bit. Their experiments on a single electron in a diamond chip could create quantum devices that are less prone to errors when operated at high speeds.
To understand their experiment, one can look to the ultimate setting for speed in classical dynamics: the oval racetracks at the Indianapolis or Daytona 500. To enable the racecars to navigate the turns at awesome speeds, the racetrack’s pavement is “banked” by up to 30 degrees. Newtonian mechanics could explain that this inward slope of the pavement allows the normal force provided by the road to help cancel the car’s centrifugal acceleration, or its tendency to slide outward from the turn. The greater the speed, the greater the bank angle that is required.
“The dynamics of quantum particles behave analogously,” said Aashish Clerk, professor of theoretical physics at McGill University. “Although the equations of motion are different, to accurately change the state of a quantum particle at high speeds, you need to design the right track to impart the right forces.”
Clerk, together with McGill postdoctoral fellows Alexandre Baksic and Hugo Ribeiro, formulated a new technique to enable faster quantum dynamics by deftly absorbing detrimental accelerations felt by the quantum particle. These accelerations, unless compensated, would divert the particle from its intended trajectory in the space of quantum states. The new theory could be used to speed up the diamond-based quantum devices.
Building the quantum fast track required shining intricately-shaped, synchronized laser pulses on single electrons trapped at defects inside their diamond chips. This experimental feat was achieved by lead author Brian Zhou, working with Christopher Yale, F. Joseph Heremans, and Paul Jerger.
“We demonstrated that these new protocols could flip the state of a quantum bit, from ‘off’ to ‘on,’ 300% faster than conventional methods,” said Awschalom, Argonne National Laboratory. “Shaving every nanosecond from the operation time is essential to reduce the impact of quantum decoherence,” he explained, referring to the process by which quantum information is lost to the environment Prof. Burkard remarked, “What is promising for translating these techniques beyond the laboratory is that they are effective even when the system is not perfectly isolated.”
The researchers anticipate that their methods can be further applied for fast and accurate control over the physical motion of atoms or the transfer of quantum states between different systems, and convey benefits to quantum applications, such as secure communications and simulation of complex systems. http://www.mcgill.ca/newsroom/channels/news/fast-track-control-accelerates-switching-quantum-bits-264827
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