Schematic of non-classical mechanical states from a resonator–qubit combination. The transmon qubit couples capacitively to the acoustic mechanical modes of a separate sapphire plate, one of which is represented as a series of blue and red antinodes. Non-classical mechanical states originate from this interaction. The three vignettes reproduce the Wigner functions of i) a compressed vibrational state, ii) a non-Gaussian vibrational state, and iii) a non-Gaussian vibrational state with large negative values of the Wigner function, a characteristic of strong nonclassicality. Credit: Taken from ref. 7, Springer Nature Ltd. Vignettes reproduced from reference no. 1, Springer Nature Ltd.
Mechanical systems are very suitable 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, namely by “squeezing” their states and introducing nonlinear effects into the quantum regime.
The research team at ETH Zurich led by Dr. Mattea Fadela recently presented a new approach to realizing quantum compression in a nonlinear mechanical oscillator. This approach, outlined in an article published in Natural physicscould have interesting implications for the development of quantum metrology and sensing technologies.
“Initially, our goal was to prepare a mechanically compressed state, specifically a quantum state of motion with reduced quantum fluctuations along a single 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 a set of universal gates for quantum computing with continuously variable systems – meaning mechanical degrees of freedom, electromagnetic fields, etc., as opposed to qubits, which are systems with discrete variables.”
As they ran their experiments, trying to get more and more squeezing, Fadel and his colleagues realized that after a certain threshold, the mechanical state becomes more than just narrower (ie, more pinched) and lengthened. Additionally, they found that the floor began to twist/twist around itself in an “S” or even “8” pattern.
“We didn’t expect this because the preparation of non-Gaussian states requires significant nonlinearities in the mechanical oscillator, so we were quite surprised, but of course 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 realize that in our device the resonator inherited some of the nonlinearity from the qubit it was connected to.”
The researchers found that the nonlinearities the resonator inherited were quite strong, leading to the fascinating effect they observed. In their recent paper, they demonstrated this new approach to realizing quantum compression in this nonlinear mechanical system.
The system used in the team’s experiments consists of a superconducting qubit connected to a mechanical resonator via a disk made of piezoelectric material. The coupling between the two systems results in an effective nonlinearity of the resonator.
“When two-tone drive is applied to the system at the correct frequencies, f1+f2= 2*fm (where f1 af2 are two-tone excitation frequencies afm frequency of the mechanical mode), a parametric process takes place: two microwave photons at frequencies f1 af2 from the drives are converted to a pair of phonons at frequency fm mechanics,” Fadel said.
“It’s very similar to the parametric conversion process in optics, where light fields are sent into a nonlinear crystal that generates compression in a similar way to what I described.”
A new approach to realizing mechanical squeezing introduced by this team of researchers could soon open up new opportunities for research and development of quantum devices. In their experiments, Fadel and colleagues also used their approach to demonstrate the preparation of non-Gaussian states of motion and confirmed that their mechanical resonator exhibits tunable nonlinearity.
“The nonlinearity we observed in our resonator is tunable because it depends on the difference between the qubit and resonator frequencies, which can be controlled in the experiment,” Fadel said.
“The realization of compressed states has important applications for quantum metrology and for processing quantum information using continuous variables. Non-Gaussian states can also be used as a source for quantum information problems and for fundamental research in quantum mechanics.”
In his future studies, Fadel hopes to further explore the possibility of realizing a mechanical quantum simulator based on the approach presented 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 sensing of forces, gravitational waves, and even tests of fundamental physics,” Fadel added. “We recently showed in 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, Natural 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 9, 2024, from https://phys.org/news/2024-07-approach-quantum-mechanical.html
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