A time-independent, parity-preserving ‘delta’ shaped potential reduces symmetry in a quantum van der Pol oscillator; this allows for generation of non-classical steady states with negative Wigner function values and enables parity-protected quantum phase locking. The energy levels lock into opposite phases due to an interaction between the defect and nonlinear dissipation channels. This method stabilizes coherences without requiring coherent driving fields, offering advantages over previous techniques using squeezing or harmonic drives.

Introducing a small, static “defect” into a quantum system creates an imperfection in its design and offers a new way to stabilise unusual quantum properties without needing complex external controls. This method breaks down symmetry within a specific type of oscillating quantum system. Researchers at Affiliation: European Laboratory for Non-linear Spectroscopy di Ottica CNR and Università di Firenze have demonstrated a novel method for stabilising unusual quantum properties in an oscillating system, bypassing complex external controls previously required.

This allows them to generate non-classical states where certain measurements yield impossible results according to everyday physics, indicated by negative values in something called the Wigner function. Key to this approach is that it also enables “quantum phase locking”, where energy levels become synchronised without needing constant external adjustments. Researchers now detail how these effects arise from an interplay between the defect and nonlinear dissipation channels, but such precise control could be scaled for more complex systems.

Engineered defects induce Z2 symmetry and enhance quantum coherence

Localized defect potentials introduced into a quantum van der Pol oscillator reduce its continuous U-symmetry to discrete Z2-symmetry; this stabilizes Wigner negativity, a signature of non-classical behaviour, to levels exceeding those achievable with parametric squeezing or harmonic drives. Parity-protected phase locking then becomes possible, where energy levels lock into opposite phases, an effect impossible in systems limited by two-photon loss mechanisms. Interactions between the engineered “defect” and nonlinear dissipation channels within the system create stationary coherences without requiring external driving fields.

Wigner negativity surpassing other methods like parametric squeezing or harmonic drives is achieved when introducing this localized defect potential. This arises from interactions between the engineered “defect” and nonlinear dissipation channels, creating stable quantum states that do not require external driving fields, a feat unattainable with typical two-photon loss limitations.

Analysis of angular phase distributions revealed peaks matching predicted locking angles; these findings confirm the observed coherences alongside equivalence (as shown by diagnostic quantifiers S2 and R2) during peak analysis of P(θ). Furthermore, introducing this defect opens a Liouvillian spectral gap, measuring how quickly a system settles into its final state, accelerating relaxation towards the locked phase compared to an unperturbed oscillator.

Engineering Symmetry Protected States Despite Photon Recoil Challenges

A compelling experimental setup using ultracold atoms in optical tweezers is proposed for scaling this approach; however, important hurdles remain even as this technique proves fruitful for quantum simulation. Maintaining precise control over state-selective interactions alongside Raman sidebands presents technical demands when creating the necessary localized defect. The abstract acknowledges potential issues with photon recoil inducing unwanted heating effects that could disrupt these fragile states, but offers only broad statements about beam direction and transition characteristics as mitigation strategies.

Despite challenges in precisely controlling atomic systems, specifically managing unwanted heating from photon recoil during manipulation, this work provides a novel pathway to engineer strong quantum states protected by symmetry principles. Researchers at the European Laboratory for Non-linear Spectroscopy have demonstrated a method to stabilise uniquely quantum states within an oscillating system; their proposal involves introducing a carefully engineered “defect,” specifically a parity-preserving delta-shaped potential, which alters the symmetry of a van der Pol oscillator from continuous to discrete form. This reduction in symmetry allows for generating non-classical steady states exhibiting Wigner function negativity, indicating genuinely quantum behaviour without requiring external driving fields.

Researchers successfully created stable, non-classical quantum states within an oscillating system using a designed localized defect, a parity-preserving delta-shaped potential, that altered its underlying symmetry. This manipulation resulted in protected quantum coherences and generated negative values in the Wigner function, demonstrating uniquely quantum behavior.

The team proposes realizing this with ultracold alkaline-earth-like atoms in optical tweezers, engineering the defect through state-selective contact interactions driven by Raman sidebands; they observed accelerated relaxation towards locked phases due to an induced Liouvillian spectral gap. These findings show how tailored defects can be used to control energy levels and establish phase locking within quantum oscillators.

👉 More information
🗞 Defect-induced stabilization of Wigner negativity and parity-protected phase-locking
✍️ Beatrice Donelli and Stefano Gherardini (Affiliation: European Laboratory for Non-linear Spectroscopy)
🧠 ArXiv: https://arxiv.org/abs/2611.15624

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