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Phase transitions

How does a false vacuum decay on a quantum chip?

Vodeb J, Desaules JY, Hallam A, et al. · Nature physics · 2025

Open access · cc by · source: Europe PMC

When a chain of quantum spins is pushed out of a metastable state, bubbles of the stable state form only at specific quantized sizes, and they then grow by trading spins with neighbouring bubbles rather than on their own.

Study at a glance

Design
Other — Analogue quantum simulation on a D-Wave annealer (ferromagnetic Ising ring in transverse and longitudinal fields), compared with Bloch-Redfield, matrix-product-state and effective-Hamiltonian calculations
N
No participant N; the simulator is a ring of 5,564 superconducting flux qubits, and one closed-system MPS simulation used 100 spins.
Population
Superconducting flux qubits on a D-Wave Advantage quantum annealer arranged as a 1D ring
Outcome
Magnetization and density of n-spin bubbles over time after the longitudinal field is flipped

Structured fields used in claim comparison tables when every cited study has a complete layer.

Key findings

Bubbles of flipped spins appeared only when the field matched the resonance condition where the surface cost of a bubble of n spins balances its volume gain; the team saw 1- to 6-bubble resonances and bubbles as large as about 300 spins. Magnetization curves collapsed onto single curves when time was rescaled as the theory predicts, and at the one-spin resonance neighbouring flipped spins were strongly suppressed, an emergent blockade. Large bubbles could not spread alone; they grew or shrank only by exchanging spins with a neighbouring bubble.

Methodology

The team set up a ring of 5,564 superconducting qubits on a quantum annealer to behave like a quantum Ising chain. They prepared all spins up, then flipped the sign of the longitudinal field so 'all up' became a metastable false vacuum, let the system evolve for up to a few microseconds, and read out every spin. They varied the fields, counted bubbles of flipped spins of each size, and compared with numerical simulations and effective models.

Limitations

The annealer is an open, noisy system: the longitudinal field wobbles strongly after the flip and thermalization mixes with bubble dynamics, so the authors say they cannot cleanly separate thermal effects from bubble interactions. It is a one-dimensional lattice analogue in the weak transverse-field regime, not a test of cosmological false vacuum decay itself. Later-time behaviour is shaped by the device's slow measurement ramp.

How this study connects

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