# World's largest programmable quantum simulator with 256 qubits developed by MIT researchers

#### The number of quantum states possible with 256 qubits exceeds the number of atoms in the solar system

A team of researchers working at the Harvard-MIT Center for Ultracold Atoms claims to have created the largest ever programmable quantum simulator capable of operating with 256 qubits.

This team of physicists has been working on quantum simulators for some time. In 2017, they created a 51-qubit quantum simulator using rubidium atoms that were arranged in a specific order using a one-dimensional (1D) array of individually focused laser beams (optical tweezers).

Now, the researchers have developed a much larger 256-qubit system using atoms that can be lined up in a two-dimensional (2D) array.

Quantum computers work in a fundamentally different way than classical computers. They use qubits (quantum bits) as the basic building blocks of computing.

Unlike regular binary digits (bits) that are used to store a 0 or 1 on everyday computing machines, qubits can store a combination of both through superposition.

For a quantum computer to work properly, qubits must remain 'entangled' with each other, meaning that the state of one qubit instantaneously affects the state of another qubit, even when they are physically separated from each other.

Today's quantum computers contain only a few dozens of qubits, as any attempt to add more qubits makes them prone to environmental noise, eventually disturbing the computing process and resulting in erroneous calculations.

Professor Mikhail Lukin, co-director of the Harvard Quantum Initiative and one of the authors of the study, believes that their latest breakthrough of 256-qubit quantum simulator has moved "the field into a new domain where no one has ever been to thus far".

"We are entering a completely new part of the quantum world," he said.

According to the Harvard-MIT researchers, their latest system uses an upgraded version of their earlier 51-qubit quantum simulator platform.

In the new system, atoms can be assembled in 2D arrays of optical tweezers, allowing researchers to increase the achievable system size from 51 to 256 qubits.

The atoms can be arranged in a variety of shapes, to induce different programmable interactions between them.

The system's size and its programmability put it at "the cutting edge of the race for a quantum computer," says Sepehr Ebadi, a student in the Graduate School of Arts and Sciences and lead author of the study.

"The number of quantum states that are possible with only 256 qubits exceeds the number of atoms in the solar system," Ebadi explained.

The team has already used the new quantum simulator to observe exotic quantum states of matter that were not realised in earlier experiments. They also used the simulator to perform a quantum phase transition study, shedding light on how magnetism works at the quantum level.

The researchers now want to improve the simulator by making it more programmable and enhancing laser control over the qubits.

They are also exploring how the system can be used for new applications, such as studying exotic quantum phases, non-equilibrium entanglement dynamics and hardware-efficient realisation of quantum algorithms.

The details of the research are published in the journal *Nature*.

The announcement comes a month after researchers from the Cambridge Research Laboratory of Toshiba Europe claimed in June that they had set a new quantum communication record by successfully sending quantum information over a distance of 600 km via optical fibres.

The experiments showed that it was possible to transmit qubits over hundreds of kilometres of optical fibres without disturbing the fragile quantum data encoded in the particles.

Last month, Rigetti Computing announced that it had developed the world's first multi-chip quantum processor based on a proprietary modular architecture, which could help solve key challenges in scaling toward building an entirely fault-tolerant quantum computer.