Exploring uncharted territory in quantum devices

JUN 01, 2024


1 Jun, 2024

A spin (blue ball with arrow) interacts with the surrounding bosons described by non-Gaussian states – a new computational method to accurately describe what happens inside quantum devices. Credit: Ji?í Miná?

The advancement of quantum devices is at the forefront of modern technology, with the potential to revolutionize computing, communication, 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 setting up quantum devices to achieve specific desired states, bringing us closer to unlocking the full potential of quantum technology.

Quantum devices harness the peculiar behavior of quantum particles to achieve feats that surpass the capabilities of traditional machines. These devices come in various forms, ranging from collections of superconducting circuits to lattices 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 particles of light and vibrational modes of a lattice, respectively, serve as examples of bosons.

Liam Bond, Arghavan Safavi-Naini, and Ji?í Miná? from the University of Amsterdam, QuSoft, and Centrum Wiskunde & Informatica have introduced a new approach to describe systems of spins coupled to bosons. By utilizing 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 up new possibilities for understanding and manipulating spin-boson systems.

“A Gaussian state would look like a plain red circle, without any interesting blue-red patterns,” explains PhD candidate Liam Bond. An example of a Gaussian state is laser light, in which all light waves are perfectly in sync. “If we take many of these Gaussian states and start overlapping them (so that they’re in a superposition), these beautifully intricate patterns emerge. We were particularly excited because these non-Gaussian states allow us to retain a lot of the powerful mathematical machinery that exists for Gaussian states whilst enabling us to describe a far more diverse set of quantum states.”

“There are so many possible patterns that classical computers often struggle to compute and process them. Instead, in this publication, we use a method that identifies the most important of these patterns and ignores the others. This lets us study these quantum systems and design new ways of preparing interesting quantum states,” Bond continues.

The innovative approach introduced by the Amsterdam researchers opens up a world of possibilities. It allows for the efficient preparation of quantum states, surpassing traditional methods. This fast quantum state preparation has broad applications, from quantum simulation to error correction. The researchers have 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 enhance the sensitivity of quantum sensors, hinting at the exciting potential of this method.

While these results are promising, they mark just 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 many spins and bosonic modes simultaneously, which poses a challenging but natural progression. Another focus is to consider the impact of environmental disturbances on the spin-boson systems, both of which are actively under development.

Journal reference:

  1. Liam J. Bond, Arghavan Safavi-Naini, and Ji?í Miná?. Fast Quantum State Preparation and Bath Dynamics Using Non-Gaussian Variational Ansatz and Quantum Optimal Control. Physical Review Letters, 2024; DOI: 10.1103/PhysRevLett.132.170401