Scheme of nonclassical mechanical states of a resonator-qubit combination. A transmon qubit capacitively couples to acoustic mechanical modes of a separate sapphire slab, one of which is shown as a series of blue and red antinodes. Nonclassical mechanical states emerge from this interaction. Three vignettes reproduce Wigner functions of i) a squeezed vibrational state, ii) a non-Gaussian vibrational state, and iii) a non-Gaussian vibrational state with large negative values of the Wigner function, hallmarks of strong nonclassicality. Credit: Adapted from ref. 7, Springer Nature Ltd. Vignettes reproduced from ref. 1, Springer Nature Ltd.
Mechanical systems are well suited for realizing applications such as quantum information processing, quantum sensing, and bosonic quantum simulation. However, the effective use of these systems for these applications depends on the ability to manipulate them in unique ways, in particular by “squeezing” their states and introducing nonlinear effects in the quantum regime.
A research team at ETH Zurich led by Dr. Matteo Fadel recently introduced a new approach to realize quantum squeezing in a nonlinear mechanical oscillator. This approach, outlined in a paper published in Physicscould have interesting implications for the development of quantum metrology and sensor technologies.
“Initially, our goal was to prepare a mechanically squeezed state, namely a quantum state of motion with reduced quantum fluctuations along one phase space direction,” Fadel told Phys.org. “Such states are important for quantum sensing and quantum simulation applications. They are one of the gates in the universal gate set for quantum computing with continuously variable systems, meaning mechanical degrees of freedom, electromagnetic fields, etc., in contrast to qubits which are discrete-variable systems.”
While conducting their experiments and trying to achieve increasing degrees of squeezing, Fadel and his colleagues realized that after a certain threshold, the mechanical state became more than just narrower (i.e. more squeezed) and more stretched. Furthermore, they found that the state began to twist/twirl around itself, following an “S”-like or even “8”-like pattern.
“We didn’t expect this, because preparing non-Gaussian states requires significant nonlinearities in the mechanical oscillator. So we were quite surprised, but of course also excited,” Fadel explains.
“Typical mechanical nonlinearities are extremely small and typical couplings between mechanical oscillators and light/microwave fields are also linear. However, it was easy to realize that in our device the resonator inherits some of the nonlinearity of the qubit it was coupled to.”
The researchers found that the nonlinearities inherited by the resonator were quite strong, resulting in the fascinating effect they observed. In their recent paper, they demonstrated this new approach to realizing quantum squeezing in this nonlinear mechanical system.
The system used in the team’s experiments consists of a superconducting qubit coupled to a mechanical resonator via a disk of piezoelectric material. The coupling between these two systems results in the effective nonlinearity of the resonator.
“When a two-tone drive is applied to the system at the correct frequencies,1+v2=2*vM (where f1 and f2 are the two-tone drive frequencies and fM the frequency of the mechanical mode), a parametric process takes place: two microwave photons with frequencies f1 and f2 of the drives are converted into a pair of phonons at frequency fM of the mechanics,” said Fadel.
“This is very similar to a parametric conversion process in optics, where light fields are sent into a nonlinear crystal that generates compression in a similar way to what I have described.”
The new approach to realizing mechanical compression introduced by this team of researchers could soon open up new possibilities for research and development of quantum devices. In their experiments, Fadel and his colleagues also used their approach to demonstrate the preparation of non-Gaussian states of motion and confirmed that their mechanical resonator exhibits tunable nonlinearity.
“What is striking is that the nonlinearity we observed in our resonator is tunable, because it depends on the difference between the frequencies of the qubit and the resonator. This difference can be controlled in the experiment,” Fadel said.
“The realization of squeezed states has important applications for quantum metrology and for quantum information processing using continuous variables. Non-Gaussian states can also be used as a source for quantum information tasks and for fundamental investigations of quantum mechanics.”
In his future studies, Fadel hopes to further explore the possibility of realizing a mechanical quantum simulator based on the approach introduced in this recent paper. Specifically, this simulator could exploit the ability to independently address and control dozens of bosonic modes in the team’s acoustic resonators.
“Our devices could also find interesting applications in quantum-enhanced force sensing, gravitational waves, and even tests of fundamental physics,” Fadel added. “We recently showed in a follow-up work that the mechanical nonlinearity can be so strong that it allows us to realize a mechanical qubit.”
More information:
Stefano Marti et al, Quantum squeezing in a nonlinear mechanical oscillator, Physics (2024). DOI file: 10.1038/s41567-024-02545-6
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Quote: A new approach to realizing quantum mechanical compression (2024, July 8) Retrieved July 9, 2024, from https://phys.org/news/2024-07-approach-quantum-mechanical.html
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