DATE2023.05.27 #Press Releases

A new method for quantum control

It provides a new basis for controlling quantum states using the quantum tunneling effect and has applications in quantum computation, condensed matter physics, and nuclear magnetic resonance. 

May 27, 2023

Outside of science fiction, walking through a wall is impossible. Unless you shrink down to the size of atoms and electrons. At that scale, normal laws of physics don’t apply; but quantum physics does, which can allow particles to pass through energy barriers in a process called quantum tunneling.   

For example, consider a particle such as an electron at the bottom of an imaginary bowl whose height reflects how much energy the particle needs to climb up and out of the bowl. The quantum particle dropped from the edge of the bowl has a certain probability of remaining where it is or ‘tunneling’ outside the bowl. One can control the quantum state of a particle by slowly changing the height of the energy barrier such that the particle does not tunnel. In other words, if you rock the metaphorical bowl too fast, changing its height quickly, the particle can undergo quantum tunneling. Such quantum control is a basis for controlling qubits, which are the basic unit of information in quantum computing.

Published in 1932, the Landau-Zener model links the speed of changing the barrier height to the quantum tunneling probability. So, using the model, scientists theoretically predicted that they could control the properties of quantum matter to an extent. 

A study by Sasaki and colleagues proposed a new method of quantum control that allows them to experimentally control quantum tunneling with a near 100% probability for the first time in the world. The team’s new method incorporates geometric ‘twist’ effects into the Landau-Zener model. It involves changing the energy barrier height (or the ‘driving field’) parabolically with time as defined by the ‘twisted’ Landau-Zener model (Figure 1). Their method applies to quantum systems at various energy scales, e.g., quantum computation, condensed matter physics, and nuclear magnetic resonance. 

Figure 1: How the energy barrier height changed parabolically with time as defined by the ‘twisted’ Landau-Zener model which gave the probability of quantum tunneling. (a) shows the change in energy levels and the probability of quantum tunneling. (b) shows the parabolic change of the driving field. 

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