Oxford physicists have for the first time produced and controlled quadsqueezing, a fourth‑order quantum interaction, using a single trapped ion and a novel protocol that layers two non‑commuting linear drives. The interplay of those drives generated the effect about 100 times faster than conventional approaches. This faster, more robust generation of high‑order quantum states could enable ultra‑sensitive sensors, advanced trapped‑ion quantum processors, and experimental studies of complex theories like lattice gauge models.
Oxford Physicists Produce Quadsqueezing — A Fourth‑Order Quantum Effect — 100 Times Faster Than Expected
Artist’s impression of two non-commuting forces generating nonlinear interactions. Their combined action produces richer dynamics than either force alone. Image credit: Eliza Wolfson.
Oxford researchers have experimentally produced and controlled quadsqueezing, a fourth-order quantum interaction, demonstrating the effect roughly 100 times faster than conventional expectations. The team, led by Dr. Oana Băzăvan (University of Oxford) with co-author Dr. Raghavendra Srinivas, published the work in Nature Physics.
What They Achieved
Using a single trapped ion, the group created a high-order quantum state — previously regarded as too weak and too fragile for practical observation — by layering two simple, time‑dependent forces. Rather than driving a complex fourth‑order process directly, they exploited the non‑commuting nature of the two drives so their combined action produced an effective fourth‑order interaction known as quadsqueezing.
How It Works
In quantum mechanics, the order in which operations are applied can matter: two operations A then B often produce a different result than B then A. This non‑commutativity was used deliberately. By applying two well‑controlled linear drives whose actions do not commute, the researchers engineered an amplified effective interaction that goes beyond the sum of the parts. Practically, the interplay of the drives boosted the ion's motion and generated fourth‑order squeezing on a timescale about two orders of magnitude faster than standard techniques.
"The result is more than the creation of a new quantum state. It is a demonstration of a new method for engineering interactions that were previously out of reach," said Dr. Oana Băzăvan.
Why This Matters
Second‑order squeezing is already a powerful tool: for example, squeezed light improves the sensitivity of gravitational‑wave detectors such as LIGO. Higher‑order processes like quadsqueezing can reshape quantum uncertainty in more complex ways, enabling states and measurements that are far more sensitive or that simulate richer physical models. By making these higher‑order interactions faster and more robust to noise, the new method opens practical routes to:
- Ultra‑sensitive gravitational and inertial sensors
- Improved trapped‑ion quantum processors that exploit complex motional states
- Experimental simulations of advanced theories, such as lattice gauge models, previously inaccessible to lab platforms
Outlook
The layered, non‑commuting drive protocol provides a new engineering toolkit for quantum harmonic oscillators — the building blocks of many quantum technologies. While further work is needed to scale and integrate the approach into multi‑qubit systems, the demonstration marks a significant step toward harnessing high‑order quantum effects in practical devices.
Paper: Băzăvan, O., Srinivas, R., et al., Nature Physics.
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