Vibrating atoms make robust qubits, physicists find

Vibrating atoms make robust qubits, physicists find | MIT News
Credits:Credit: Sampson Wilcox/RLE

MIT physicists have discovered a new quantum bit in the form of vibrating pairs of atoms. They discovered that when pairs of fermions are trapped in an optical lattice, they can be in two states at the same time. In this case, the atoms held a superposition of two states, in which the pair wobbled against each other while also swinging in sync.

The team was able to maintain a state of superposition among hundreds of vibrating pairs of fermions. They achieved a new system of qubits that appears to be robust over a long period of time. The discovery, published today in the journal Nature, demonstrates that wobbly qubits could be a promising foundation for future quantum computers.

A qubit is a basic unit of quantum computing. A qubit can exist in a superposition of both states where a classical bit carries out a series of logical operations. A qubit should be able to communicate with many other qubits and process multiple streams of information at the same time to solve problems that would take classical computers years to solve.

Some of the qubits are engineered and others are natural. Most qubits are unwilling to communicate with other qubits and can't maintain their superposition.

The MIT team's new qubit appears to be able to maintain a superposition between two states, even in the midst of environmental noise, for up to 10 seconds. The team believes the new vibrating qubits could be used to carry out tens of thousands of operations in the blink of an eye.

Martin Zwierlein, the Thomas A. Frank Professor of Physics at MIT, says it should take only a millisecond for these qubits to interact, so we can hope for 10,000 operations during that coherence time.

The paper was co-authored by a number of people, including a lead author, a co-author, and members of the Research Laboratory of Electronics at MIT.

Accidents are happy.

The team discovered it by chance. The behavior of atoms is studied by the group. When atoms are chilled to temperatures a millionth that of space, and isolated at densities a millionth that of air, quantum phenomena and novel states of matter can emerge.

The behavior of fermions was studied by the group of people. A fermion is a particle with an odd half-integer spin. Fermions are prickly by nature. The Pauli exclusion principle states that no two fermions can be in the same quantum state. One fermion must spin down if it spins up.

The structure of atoms, the diversity of elements, and the stability of the universe are all caused by the mutual Pauli exclusion of fermions. Any type of atom with an odd number of particles would repel each other.

The team was studying fermionic atoms. They used a system of lasers to create an optical lattice to trap the atoms after cooling a cloud of fermions. They adjusted the conditions so that each well trapped a pair of fermions. They observed that under certain conditions, each pair of fermions appeared to move in sync.

MIT physicists find that pairs of atoms can hold a superposition of two vibrational states. Like two swinging pendula, the atoms can move in sync, and against each other, at the same time, making them robust qubits for quantum computing. Credit: Courtesy of the researchers

After giving each fermion pair a kick, they took images of the atoms in the lattice and saw that most squares went dark. As they continued to look at the system, the atoms seemed to reappear, indicating that the pairs were in two different states.

It is often in experimental physics that you have a bright signal and the next moment it goes to hell. There is a coherent superposition evolving over time. That was a happy moment.

A low hum.

Physicists confirmed that the fermion pairs were holding a superposition of two states, like two pendula swinging in sync, and also relative to each other.

The two states are at about 144 hertz.

The team was able to control the states of the fermion pairs by applying and varying a magnetic field.

By applying a magnetic field, we can vary the strength of the spring between the two pendulas and push them apart.

About 400 fermion pairs were simultaneously manipulated. The group of qubits had a state of superposition for up to 10 seconds before individual pairs collapsed into one or the other state.

We have full control over the states of these qubits.

To make a functional quantum computer using vibrating qubits, the team will have to find ways to also control individual fermion pairs. Finding a way for individual qubits to communicate with each other will be the bigger challenge. There are some ideas that Zwierlein has.

He says that there are ways to lower the barrier between pairs so that they can interact. There is a path that leads to a two-qubit gate, which is what you would need to make a quantum computer.

The National Science Foundation, the Gordon and Betty Moore Foundation, the Vannevar Bush Faculty Fellowship, and the Alexander von Humboldt Foundation supported the research.

More information: Thomas Hartke, Quantum register of fermion pairs, Nature (2022). DOI: 10.1038/s41586-021-04205-8. Journal information: Nature Citation: Vibrating atoms make robust qubits, physicists find (2022, January 26) retrieved 26 January 2022 from This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only.