A Unique Approach to Achieving Quantum Mechanical Squeezing

Applications including bosonic quantum simulation, quantum information processing, and quantum sensing are well suited for mechanical systems. However, the capacity to manipulate these systems in novel ways—that is, by “squeezing” their states and producing nonlinear effects in the quantum regime—is essential to their effective usage for these applications.

Dr. Matteo Fadel’s research group at ETH Zurich has unveiled a novel method for achieving quantum squeezing in a nonlinear mechanical oscillator. This method, described in research that was published in Nature Physics, may have intriguing ramifications for the advancement of sensing and quantum merology.

“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 stated to 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 systematizing mechanical degrees of freedom, electromagnetic fields, etc., as opposed to qubits that are discrete-variable systems.”

Fadel and his colleagues noticed that the mechanical condition was becoming more elongated and more than just narrower (more squeezed) after reaching a specific threshold when doing their experiments and attempting to achieve an increasing degree of squeezing. Furthermore, they discovered that the condition began to spiral or twist around itself in a “S” or even “8” shape.

“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 of course also excited,” Fadel said.

“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 was inheriting some of the nonlinearity from the qubit it was coupled to.”

The intriguing impact that the researchers saw was caused by the resonator’s significant inherited nonlinearities, they discovered. They demonstrated this novel method of achieving quantum squeezing in this nonlinear mechanical system in a recent study.

The setup used in the group’s research includes a mechanical resonator and a superconducting qubit connected by a piezoelectric disk. The resonator’s effective non linearity arises from the interaction between these two systems.

“When a two-tone drive is applied to the system at the correct frequencies, f1+f2=2*fm (where f1 and f2 are the two-tone drive frequencies and fm is the frequency of the mechanical mode), a parametric process takes place: two microwave photons at frequencies f1 and f2 from the drives are converted into a pair of phonons at frequency fm of the mechanics,” Fadel stated.

“This is very similar to a parametric conversion process in optics, where light fields are sent to a nonlinear crystal that generates squeezing in a similar way as I described.”

This group of researchers has developed a novel method for achieving mechanical squeezing, which may soon lead to new avenues for investigation and the advancement of quantum devices. Fadel and his associates verified that their mechanical resonator demonstrates controllable nonlinearity and utilized their method to generate non-gaussian states of motion in their experiments.

“Notably, the nonlinearity we observed in our resonator is tunable, as it depends on the difference between qubit and resonator frequencies, which can be controlled in the experiment,” Fadel stated.

“The realization of squeezed states has important applications for quantum merology and for quantum information processing using continuous variables. Non-gaussian states can also be used as a resource for quantum information tasks and for fundamental investigations of quantum mechanics.”

Based on the methodology presented in this latest study, Fadel intends to explore the feasibility of implementing a mechanical quantum simulator in his future research. In particular, the simulator might take advantage of the team’s acoustic resonators’ ability to address and control tens of bosonic modes separately.

“Our devices could also find interesting applications in quantum-enhanced sensing of forces, gravitational waves, and even tests of fundamental physics,” Fadel stated. “Recently, we showed in follow-up work that the mechanical nonlinearity can be so strong that it allows us to realize a mechanical qubit.”

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