Electromagnetic waveguides on diamond-based chips Used to Manipulate Quantum States at Gigahertz Rates

Physicists at UC Santa Barbara have made an important advance in electrically controlling quantum states of electrons, a step that could help in the development of quantum computing.

In seperate research, another group controlled spin electronically

The researchers have demonstrated the ability to electrically manipulate, at gigahertz rates, the quantum states of electrons trapped on individual defects in diamond crystals. This could aid in the development of quantum computers that could use electron spins to perform computations at unprecedented speed.

Using electromagnetic waveguides on diamond-based chips, the researchers were able to generate magnetic fields large enough to change the quantum state of an atomic-scale defect in less than one billionth of a second. The microwave techniques used in the experiment are analogous to those that underlie magnetic resonance imaging (MRI) technology.

The key achievement in the current work is that it gives a new perspective on how such resonant manipulation can be performed. “We set out to see if there is a practical limit to how fast we can manipulate these quantum states in diamond,” said lead author Greg Fuchs, a postdoctoral researcher at UCSB. “Eventually, we reached the point where the standard assumptions of magnetic resonance no longer hold, but to our surprise we found that we actually gained an increase in operation speed by breaking the conventional assumptions.”

While these results are unlikely to change MRI technology, they do offer hope for the nascent field of quantum computing.

Science Magazine: Gigahertz Dynamics of a Strongly Driven Single Quantum Spin

Two-level systems are at the core of numerous real-world technologies such as magnetic resonance imaging and atomic clocks. Coherent control of the state is achieved with an oscillating field that drives dynamics at a rate determined by its amplitude. As the strength of the field is increased, a different regime emerges where linear scaling of the manipulation rate breaks down and complex dynamics are expected. Employing a single spin as a canonical two-level system, we have measured the room-temperature “strong-driving” dynamics of a single nitrogen vacancy center in diamond. Using an adiabatic passage to calibrate the spin rotation, we observe dynamics on subnanosecond time scales. Contrary to conventional thinking, this breakdown of the rotating wave approximation provides opportunities for time-optimal quantum control of a single spin.

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