Nondestructive Testing in a Quantum System

quantum chip hybrid device
The team's hybrid device with an acoustic resonator chip on top of a superconducting qubit chip. (von Lüpke et al., Nat Phys, 2022)

There is an important aspect of quantum computing that you may not have considered before. These measurements, called 'quantum non-destructive or non-destructive measurements', refer to observing certain quantum states without destroying them in the process. If we want to put together a working quantum computer, we will have to make an extraordinary effort to keep information from being scattered every second while calculations are made. So, how can this be possible with an objective approach without thinking subjectively?

Now, scientists have described a very promising new technique for recording quantum nondestructive measurements.

Mechanical quantum systems – elements that are somewhat large for quantum computing but extremely small for us – were the subject of this study.

They can be manipulated by basic quantum magic by mechanical motion (like vibration) and integrated with other quantum systems as well. “Our findings pave the way for the application of more complex quantum algorithms using mechanical systems such as quantum error correction and multimodal operations,” the researchers write in their paper.

“Our results open the door to realize more complex quantum algorithms using mechanical systems such as quantum error correction and multimodal operations,” the researchers explain in their published paper.

For this experiment, the researchers created a narrow strip of high-quality sapphire that was just over half a millimeter thick. Acoustic waves, energy units that act like phonons that can be pushed through quantum computing processes, were excited using a small piezoelectric transducer. Acoustic resonator is the technical term for this device.

What is Phonon?

In physics, a phonon is a collective excitation in a periodic, elastic arrangement of atoms or molecules in condensed matter, especially solids and some liquids.

The phonon, a type of semiparticle, is an excited state in the quantum mechanical quantization of vibrational modes for the elastic structures of interacting particles. Phonons can be thought of as quantized sound waves, similar to photons as quantized light waves.

Studying phonons is an important part of condensed matter physics. They play an important role in many physical properties of condensed matter systems, such as thermal conductivity and electrical conductivity, and also play a fundamental role in neutron scattering patterns and related effects.

The concept of the phonon was introduced in 1932 by the Soviet physicist Igor Tamm. The name phonon comes from the Greek word φωνή (phonē), meaning sound or sound, because long wavelength phonons cause sound. Its name is similar to the word photon.

If we go back to our article;

This was the first step in the process. The acoustic resonator is paired with a superconducting qubit, which can hold both 1 and 0 simultaneously to make the measurements, fundamental quantum computer building blocks with which businesses like Google and IBM have previously built primitive quantum computers.

The scientists were able to read the number of phonons in the acoustic resonator without interacting with them or transmitting any energy, by making the state of the superconducting cuboid dependent on their quantity.


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Putting together the quantum computational equivalent wasn't easy: The way these states were extended to longer times was part of the innovation in this technique. Quantum states are usually fairly short-lived. This was accomplished partly by the choice of materials and partly by the use of a superconducting aluminum chamber that provides electromagnetic shielding.

In subsequent trials, they were able to obtain the 'parity measure' of the mechanical quantum system.

The parity measure is important in a number of quantum technologies, especially when it comes to fixing system errors — and no computer can function effectively if it always fails.

“Circuit quantum acoustodynamics can connect mechanical resonators to superconducting circuits, making a set of fundamental tools available for manipulating and detecting mobile quantum states,” the researchers write.

This is all pretty high-level quantum physics, but the gist is that this is an important step forward in one of the technologies that could potentially be the foundation for future quantum computers, especially in terms of mixing multiple types of systems.

A hybrid qubit resonator device like the one reported in this paper could combine the best of two research areas: superconducting qubit processing capability and mechanical system stability. Scientists have now shown that information can be retrieved from such a device without harm.

There is still a lot of work to be done – once the task of measuring states has been refined and completed, these states must be exploited and controlled to have practical value – but quantum computing systems may be one step closer to fulfilling their enormous promise.

The researchers add: "Here we construct direct measurements of the phonon number distribution and parity of non-classical mechanical states."

“Some of the fundamental building blocks for making acoustic quantum memory and processors are these measurements.”

Source: Sciencealert

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