A record-breaking experience can solve a huge quantum computing challenge

Two atoms that have been amplified to nearly comical size and cooled to a fraction above absolute zero have been used to create an insanely fast and powerful quantum gate that could help overcome some of the persistent challenges of quantum computing.

Since the 2-qubit gate is the basic building block of efficient quantum computers, this hack has enormous implications. It could lead to a new type of quantum computer architecture that breaks the current limitations of noise-free quantum processes.

Qubit is a contraction, short for the term “quantum bit”. It is the quantum computing equivalent of the classical qubit – the basic unit of information upon which computing technology is based.

To solve a problem the old-fashioned way, the information (and the logic used to calculate it) is represented by a binary system. Like a light switch, the component units of this system are all in an exclusive state of on or off. Or, as it is often described, as one or zero.

What makes quantum computing even more powerful is that qubits can be simultaneously, as a state known as quantum superposition. A qubit alone is not considered a computer. Combined (or entangled) with superpositions of other qubits, they can represent some very powerful algorithms.

A two-qubit gate is a logic operation that depends on the quantum state of two entangled qubits. It is the simplest component of a quantum computer, allowing qubits to be entangled and read.

Scientists have experimented with quantum gates based on different materials for some time, and have made some unusual breakthroughs. However, one problem continued to be significant: superpositions of qubits can decay quickly and easily thanks to external sources that also become entangled.

Gate acceleration is the best way to solve this problem: since this snooping is generally slower than a millionth of a second (one microsecond), a quantum gate faster than this would be able to “override” the noise to produce accurate calculations.

To take a direction toward this goal using a slightly different approach than usual, a team of researchers led by physicist Yeelai Chew of the National Institutes of Natural Sciences in Japan turned to a complex setup.

The qubits themselves are atoms of the metal rubidium in its gaseous state. Using a laser, these atoms were cooled to nearly absolute zero and placed at a precise micron-scale distance from each other using optical tweezers – lasers that can be used to manipulate atomic-scale objects.

Then the physicists pushed the atoms with a laser. This pushed electrons from the closest orbital distance to each atomic nucleus into an extremely wide orbital spacer, blowing the atoms into bodies known as Rydberg atoms. This produced a 6.5 nanosecond periodic exchange of the orbital shape and electron energy between the now massive atoms.

Using more laser pulses, the research team was able to perform a quantum gate operation between the two atoms. The speed of this process was 6.5 billionths of a second (nanoseconds) — more than 100 times faster than any previous experiments with Rydberg atoms, the researchers said, setting a new record for quantum gates based on this particular type of technology.

This doesn’t quite beat the overall record for the fastest two-qubit quantum gate operations to date. This was achieved in 2019, using phosphorous atoms in silicon, achieving a staggering 0.8 nanoseconds; But the new work involves a different approach that could sidestep some of the limitations of other species currently under development.

In addition, exploring different architectures can lead to clues that help reduce the shortcomings of other types of devices.

The team said the next steps are fairly straightforward. They need to replace a commercial laser with a purpose-built one, in order to improve accuracy, as lasers can contribute to noise; and implement better control techniques.

The search was published in Nature Photonics.

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