Exploring uncharted territories with quantum devices

The development of quantum devices is at the vanguard of modern technology and has the potential to revolutionize computing, communications and sensing.

Many modern quantum devices rely on qubits, or spins, with two energy states: “0” and “1.” However, these spins interact with bosons (photons and phonons) in real devices, leading to more complex calculations.

Researchers from Amsterdam have made a significant breakthrough in effectively describing the complex interactions of spins with bosons in quantum systems. This method could pave the way for efficiently configuring quantum devices to achieve specific desired states, bringing us closer to unlocking the full potential of quantum technology.

Quantum devices use the special behavior of quantum particles to achieve feats beyond the capabilities of traditional machines. These devices come in a variety of forms, ranging from collections of superconducting circuits to networks of atoms or ions controlled by lasers or electric fields.

Regardless of their physical form, quantum devices are often simplified as a network of interacting two-level quantum bits or spins. However, these spins also interact with their surroundings, such as light in superconducting circuits or oscillations in atomic or ionic lattices. Photons and phonons, which are light particles and lattice vibrational modes respectively, serve as examples of bosons.

Liam Bond, Arghavan Safavi-Naini and Jiří Minář from the University of Amsterdam, QuSoft and Centrum Wiskunde & Informatica introduced a new approach to describing systems of spins coupled to bosons. By using non-Gaussian states, which are combinations of simpler Gaussian states, they aim to address the lack of computational tools for such systems. Their work opens new possibilities for understanding and manipulating spin-boson systems.

“The Gaussian state would look like a plain red circle, without any interesting blue-red patterns” explains PhD student Liam Bond. An example of the Gaussian state is laser light, in which all light waves are perfectly synchronized. “If we take many of these Gaussian states and start superimposing them (so that they form a superposition), these beautifully complex patterns emerge. We were particularly excited because these non-Gaussian states allow us to retain much of the powerful mathematical machinery that exists for Gaussian states, while allowing us to describe a much more diverse set of quantum states.”

“There are so many possible patterns that classical computers often have difficulty calculating and processing them. Instead, in this paper we use a method that identifies the most important of these patterns and ignores the rest. This allows us to study these quantum systems and design new ways to prepare interesting quantum states.” Bond continues.

The innovative approach introduced by Amsterdam researchers opens up a world of possibilities. It allows for the efficient preparation of quantum states, going beyond traditional methods. This rapid quantum state preparation has a wide range of applications, from quantum simulation to error correction. Scientists demonstrated the use of non-Gaussian states to prepare critical quantum states corresponding to a system undergoing a phase transition. These critical states can significantly increase the sensitivity of quantum sensors, indicating the exciting potential of this method.

While these results are promising, they mark only the beginning of more ambitious goals. Currently, the method has been demonstrated for a single spin. The next step is to extend this to include multiple spins and bosonic modes simultaneously, which is a challenging but natural progression. Another goal is to consider the impact of environmental perturbations on spin-boson systems that are actively being developed.

Magazine number:

1. Liam J. Bond, Arghavan Safavi-Naini and Jiří Minář. Fast quantum state preparation and bath dynamics using non-Gaussian variational ansatz and optimal quantum control. Physical Inspection Letters, 2024; DOI: 10.1103/PhysRevLett.132.170401