Quantum echoes: A revolutionary method of storing information as sound waves

Quantum computing, like traditional computing, requires a method to store the information it uses and processes. On the computer you’re using right now, information—whether it’s pictures of your dog, a reminder about a friend’s birthday, or the words you type in your browser’s address bar—must be stored somewhere. Quantum computing, a relatively new field, is still investigating where and how to store quantum information.

Innovative method for storing quantum information

In a paper recently published in the journal Natural physics, Mohammad Mirhosseini, assistant professor of electrical engineering and applied physics at the California Institute of Technology (Caltech), demonstrates a new method his lab developed to efficiently convert electrical quantum states into sound and vice versa. This type of translation could enable the storage of quantum information compiled by future quantum computers, which will likely be made of electrical circuits.

Mohammad Mirhosseini and his team have introduced an innovative method to store quantum information by converting electrical quantum states into sound. The new technique utilizes phonons and avoids the energy loss associated with previous methods. It enables longer storage durations and represents a significant advance in quantum computing. Credit: Maayan Illustration

This method makes use of what are known as phonons, the sound equivalent of a light particle called a photo. (Remember that in quantum mechanics all waves are particles and vice versa). The experiment investigates phonons for storing quantum information because it is relatively easy to build small devices that can store these mechanical waves.

Using sound waves to store information

To understand how a sound wave can store information, imagine an extremely echoic room. Now, let’s say you need to remember your grocery list for the afternoon, so you open the door to that room and yell, “Eggs, bacon, and milk!” and close the door. An hour later, when it’s time to go to the grocery store, you open the door, poke your head in, and hear your own voice still echoing, “Eggs, bacon, and milk!” You just used sound waves to store information.

Mohammad Mirhosseini. Credit: Caltech

Of course, in the real world, an echo like that wouldn’t last very long, and your voice might end up being so distorted that you can no longer see your own words, not to mention that you’re using a whole space to store a small bit of data would be ridiculous. The research team’s solution is a tiny device consisting of flexible plates that are vibrated by sound waves at extremely high frequencies. When an electrical charge is placed on these plates, they become able to interact with electrical signals that carry quantum information. This allows that information to be fed into the device for storage and sent out for later use – not unlike the door to the room you yelled into earlier in this story.

Previous research and new developments

According to Mohammad Mirhosseini, previous studies had investigated a special type of materials known as piezoelectrics as a means of converting mechanical energy into electrical energy in quantum applications.

“However, these materials tend to cause energy loss for electric and sound waves, and loss is a big killer in the quantum world,” says Mirhosseini. In contrast, the new method developed by Mirhosseini and his team is independent of the properties of specific materials, making it compatible with established quantum devices based on microwaves.

Conclusion: Progress and challenges

Creating efficient storage devices with small footprints has been another practical challenge for researchers working on quantum applications, says Alkim Bozkurt, a graduate student in Mirhosseini’s group and the lead author of the paper.

“However, our method enables the storage of quantum information from electrical circuits for durations two orders of magnitude longer than other compact mechanical devices,” he adds.

Reference: “A quantum electromechanical interface for long-lived phonones” by Alkim Bozkurt, Han Zhao, Chaitali Joshi, Henry G. LeDuc, Peter K. Day and Mohammad Mirhosseini, 22 June 2023, Natural physics.
DOI: 10.1038/s41567-023-02080-w

Co-authors include Chaitali Joshi and Han Zhao, both postdoctoral researchers in electrical engineering and applied physics; and Peter Day and Henry LeDuc, who are researchers at the Jet Propulsion Laboratory, which Caltech directs NASA. The research was partly funded by the KNI-Wheatley Scholars programme.