Fig. 1: Realizing false vacuum decay on a quantum annealer.
From: Stirring the false vacuum via interacting quantized bubbles on a 5,564-qubit quantum annealer
a, Semiclassical energy landscape V as a function of magnetization M of a ferromagnetic Ising chain in transverse (hx) and longitudinal (hz) fields. The landscape exhibits a local metastable minimum dubbed as the false vacuum, represented by the polarized |↑↑…↑〉 state. The global minimum or true vacuum is the other polarized |↓↓…↓〉 state. The false vacuum decay unfolds via the creation of quantized true vacuum bubbles of size n, determined by the energy balance between the surface (4J) and volume (2hzn) energy contributions. b, False vacuum decay observation protocol. We initialize all the qubits in the |↑↑…↑〉 state by setting hz > 0 and adiabatically switch hx from 0 to a small value (hx ≪ J) over time t1 = 10 μs. Then, we flip the sign of hz, swapping the true and false vacuum states, and observing the dynamics for time t ≡ t2 – t1. Finally, we turn hx back to 0 as fast as possible (t3 – t2 ≳ 0.18 μs) and measure the spin configuration in the \({\hat{\sigma }}^{z}\) basis. This protocol is repeated 1,000 times for each value of t. c, Embedding of a 5,564-qubit ring on the Pegasus graph of the 5,614-qubit device D-Wave Advantage_system5.4, located in Jülich, Germany. The Pegasus graph contains 15 × 15 × 3 eight-qubit Chimera cells with complete bipartite connectivity (coloured crosses) that are coupled by additional external and odd couplers (grey lines)57, such that each qubit is, on average, connected to 15 other qubits. Qubits within the eight-qubit cells are connected along randomly sampled one-dimensional chains (inset). d, Spin configurations measured in our quantum simulation. The inner ring shows the initial false vacuum state comprising 5,564 spins (for clarity, only 1,000 out of 5,564 spins in a single configuration are shown). The outer three rings show configurations measured at hz = –0.1, –0.5 and –2 with hz decreasing radially. An example of a large n = 306 quantized bubble shown in purple highlights the extent of the observed bubble sizes. e, Magnetization M heat profile versus time t and longitudinal-field magnitude hz at transverse-field strength of hx = 0.002. The colour scheme is split into two separate linear scales, a larger scale from –1 to 0.999 (bottom half) and a smaller scale from 0.999 to 1 (top half). The adiabatic dynamics and the n = 1-bubble resonance are easily observed on the larger scale, whereas the n = 2-bubble resonance can only be resolved in the fourth decimal of M due to the decrease in the rate of dynamics by an order of magnitude. The apparent resonance at hz = –4 is identified with adiabatic dynamics rather than bubble creation, in which the system follows an instantaneous ground state during the evolution.
