Schematic of nonclassical mechanical states from a resonator-qubit combination. A transmon qubit is condentially coupled to the mechanical acoustic modes of a separate sapphire plate, one of which is represented as a series of blue and red antinodes. Nonclassical mechanical states arise from this interaction. Three vignettes reproduce the 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, characteristic of strong nonclassicality. Credit: Adapted from ref. 7, Springer Nature Ltd. Lines reproduced from ref. 1, Springer Nature Ltd.
Mechanical systems are well suited for realizing applications such as quantum information processing, quantum sensing, and quantum bosonic simulation. Effective use of these systems for these applications, however, relies on the ability to manipulate them in unique ways, particularly by ‘squeezing’ their states and introducing nonlinear effects in the quantum regime.
A research team at ETH Zurich led by Dr. Matteo Fadel recently presented a new approach to realize quantum squeezing in a nonlinear mechanical oscillator. This approach, described in a paper published in Nature Physicsmay have interesting implications for the development of quantum metrology and sensing technologies.
“Initially, our goal was to prepare a mechanically squeezed state, namely a quantum state of motion with reduced quantum fluctuations along a 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 continuous variable systems—meaning mechanical degrees of freedom, electromagnetic fields, etc., as opposed to qubits which are discrete variable systems.”
As they conducted their experiments and tried to achieve an increasing amount of squeeze, Fadel and his colleagues realized that after a certain threshold, the mechanical state was becoming more than just tighter (ie, more squeezed) and more extended In addition, they found that the state began to twist/rotate around itself, following an “S” or even “8”-like pattern.
“We did not expect this, as the preparation of non-Gaussian states requires significant nonlinearities in the mechanical oscillator, so we were quite surprised, but certainly also excited,” explained Fadel.
“Typical mechanical nonlinearities are extremely small, and typical couplings between mechanical oscillators and light/microwave fields are also linear. However, it was easy to see that in our device the resonator was inheriting some of the nonlinearity from the qubit it was coupled to. “
The researchers found that the nonlinearities the resonator inherited were quite strong, resulting in the fascinating effect they observed. In their recent paper, they demonstrated this new approach to realize 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 made of a piezoelectric material. The coupling between these two systems results in the effective nonlinearity of the resonator.
“When a two-color drive is applied to the system at the proper frequencies, p1+ p2=2*pm (where p1 and p2 are the two-tone driving frequencies and fm frequency of the mechanical mode), a parametric process takes place: two microwave photons at frequencies f.1 and p2 from the discs are converted into a pair of phonons with frequency fm of mechanics,” said Fadel.
“This is very similar to a parametric conversion process in optics, where light fields are sent to a nonlinear crystal that generates compression in a similar way as I described.”
The new approach to realizing mechanical squeezing introduced by this team of researchers may soon open up new opportunities for quantum device research and development. 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.
“Notably, the nonlinearity we observed in our resonator is tunable, as it depends on the difference between the cube and resonator frequencies, which can be controlled in 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 investigate the possibility of realizing a quantum mechanical simulator based on the approach presented in this latest paper. Specifically, this simulator can exploit the possibility of independent addressing and control of dozens of bosonic modes in the team’s acoustic resonators.
“Our devices may also find interesting applications in quantum-enhanced force sensing, gravitational waves and even tests of fundamental physics,” Fadel added. “Recently, we showed in follow-up work that mechanical nonlinearity can be strong enough to allow us to realize a mechanical qubit.”
More information:
Stefano Marti et al, Quantum squeezing in a nonlinear mechanical oscillator, Nature Physics (2024). DOI: 10.1038/s41567-024-02545-6
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citation: A new approach to realize quantum mechanical squeezing (2024, July 8) Retrieved July 10, 2024 from https://phys.org/news/2024-07-approach-quantum-mechanical.html
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