[Paper Review] Observing the fate of the false vacuum with a quantum laboratory

Steven Abel, Michael Spannowsky|arXiv (Cornell University)|Jun 10, 2020

Quantum and electron transport phenomenaPhysics and Astronomy48 references65 citations

TL;DR

This paper demonstrates the first experimental observation of instanton-mediated quantum tunnelling in a freely chosen quantum field theory using a quantum annealer. By encoding a scalar field theory as a generalized Ising model, the authors measure tunnelling probabilities from a false vacuum to a true vacuum, achieving agreement with theoretical WKB predictions and establishing quantum annealers as viable quantum laboratories for nonperturbative field theory dynamics.

ABSTRACT

We design and implement a quantum laboratory to experimentally observe and study dynamical processes of quantum field theories. Our approach encodes the field theory as an Ising model, which is then solved by a quantum annealer. As a proof-of-concept, we encode a scalar field theory and measure the probability for it to tunnel from the false to the true vacuum for various tunnelling times, vacuum displacements and potential profiles. The results are in accord with those predicted theoretically, showing that a quantum annealer is a genuine quantum system that can be used as a quantum laboratory. This is the first time it has been possible to experimentally measure instanton processes in a freely chosen quantum field theory. This novel and flexible method to study the dynamics of quantum systems can be applied to any field theory of interest. Experimental measurements of the dynamical behaviour of field theories are independent of theoretical calculations and can be used to infer their properties without being limited by the availability of suitable perturbative or nonperturbative computational methods. In the near future, measurements in such a quantum laboratory could therefore be used to improve theoretical and computational methods conceptually and may enable the measurement and detailed study of previously unobserved quantum phenomena.

Motivation & Objective

• To establish a quantum annealer as a scalable, flexible platform for experimentally probing nonperturbative quantum field theory dynamics.
• To overcome limitations of traditional computational methods—especially in nonperturbative regimes—by replacing theoretical calculations with physical quantum experiments.
• To demonstrate the feasibility of observing instanton processes, such as false vacuum decay, in a controlled, tunable quantum system.
• To provide a framework for measuring previously unobserved quantum phenomena like solitons and instantons in arbitrary field theories.
• To calibrate and validate the quantum annealer as a quantum laboratory by comparing experimental tunnelling rates with theoretical predictions.

Proposed method

• Encoding a d = 1 scalar field theory as a generalized Ising model on a quantum annealer, with the field φ mapped to qubit degrees of freedom.
• Designing a double-Pöschl-Teller potential using the Hamiltonian H = H_0 + k(t)H_int, where k(t) is time-dependent to adiabatically turn on the true vacuum minimum.
• Initializing the system in the ground state of a Pöschl-Teller potential (ψ₀ ∝ sech^λ φ) to simulate a false vacuum state.
• Using adiabatic quantum annealing to evolve the system from the false vacuum to the true vacuum, enabling tunnelling to be observed as a function of time.
• Measuring the probability of tunnelling from the false vacuum to the true vacuum for various values of vacuum displacement v, tunnelling time, and potential profiles.
• Calibrating the effective mass and energy scale (γ = ℏ²/2mη₀²) via comparison with WKB-theoretical predictions for tunnelling rates.

Experimental results

Research questions

• RQ1 Can a quantum annealer be used to experimentally observe and measure nonperturbative quantum tunnelling processes in a scalar field theory?
• RQ2 To what extent do experimentally measured tunnelling probabilities from a false vacuum to a true vacuum agree with theoretical predictions based on the WKB approximation?
• RQ3 Can the quantum annealer serve as a general-purpose quantum laboratory for arbitrary quantum field theories with tunable interactions and vacuum structures?
• RQ4 What are the limitations of current quantum hardware in simulating and measuring instanton-like processes in quantum field theories?
• RQ5 Can experimental measurements in such a quantum laboratory reveal new quantum phenomena not yet predicted by existing theoretical frameworks?

Key findings

• The experimental tunnelling probabilities measured on the D-Wave quantum annealer show excellent agreement with theoretical predictions derived from the WKB method, validating the quantum nature of the observed processes.
• The study successfully demonstrates the first experimental observation of instanton-mediated tunnelling in a freely chosen quantum field theory, marking a milestone in experimental quantum field theory.
• The method enables the measurement of nonperturbative decay processes in scalar field theories, including tunnelling from a false vacuum to a true vacuum with adjustable potential profiles.
• The calibration of the effective field theory parameters (e.g., γ = ℏ²/2mη₀²) was achieved through comparison with WKB predictions, confirming the consistency of the quantum annealer as a physical simulator.
• The results confirm that quantum annealers can function as genuine quantum laboratories for field theories, independent of theoretical or computational approximations.
• The approach is scalable in principle, limited only by qubit count and connectivity, and opens the door to studying complex phenomena such as solitons, instantons, and sphaleron transitions in future experiments.