Harnessing spin-qubit decoherence to probe strongly-interacting quantum systems

TL;DR

The paper demonstrates that a single spin-qubit can serve as a sensitive probe of a strongly interacting XXZ spin chain, with the qubit coherence encoding information about the chain's phase boundaries and perturbation-propagation velocity. By combining time-dependent variational principle (TDVP) simulations with second-order time-convolutionless (TCL) theory and analytic limits at $\Delta=0$ and $\Delta\to\pm\infty$, the authors reveal non-Markovian decoherence in a many-body environment and a regime where the chain behaves as an effective two-level system. The qubit dynamics thus reflects both quantitative chain properties (e.g., correlation functions) and qualitative features such as bipartite entanglement entropy and phase transitions, accessible via a simple, scalable measurement of the single qubit. This approach holds potential for noninvasively diagnosing large, strongly correlated quantum systems and extracting dynamical information like information-propagation velocity from minimal experimental overhead.

Abstract

Extracting information from quantum many-body systems remains a key challenge in quantum technologies due to experimental limitations. In this work, we employ a single spin qubit to probe a strongly interacting system, creating an environment conducive to qubit decoherence. By focusing on the XXZ spin chain, we observe diverse dynamics in the qubit evolution, reflecting different parameters of the chain. This demonstrates that a spin qubit can probe both quantitative properties of the spin chain and qualitative characteristics, such as the bipartite entanglement entropy, phase transitions, and perturbation propagation velocity within the system. This approach reveals the power of small quantum systems to probe the properties of large, strongly correlated quantum systems.

Figures (4)

• Figure 1: The spin-qubit probe coupled to a strongly correlated quantum spin chain. The chain acts as an environment for the qubit, which facilitates decoherence, while the qubit introduces a perturbation to the chain propagating in the system. The propagation depends on system properties and consequently determines qubit dynamics. Thus the information about the chain becomes encoded in the coherence dynamics, which can be easily measured and analyzed.
• Figure 2: Left: Evolution of qubit coherence for different values of the anisotropy parameter (TDVP - solid lines, TCL - dashed lines): (a) positive $|\Delta|\le 1$; (b) positive $|\Delta|> 1$; (c) negative $|\Delta|\le 1$; (d) negative $|\Delta|> 1$. Right: Dependence of (e) the qubit recoherence time $t_r$, (f) oscillation frequency $\omega$, (g) and entanglement entropy $S$ on anisotropy parameter $\Delta$. Dependence of qubit recoherence time $t_r$ on $L$ (h).
• Figure 3: (a) Qubit decoherence for different values of $\Delta\approx -1$ (solid lines - TDVP, dashed lines - TCL).
• Figure 4: Decoherence curves for set $\Delta = 0$ (left) and $\Delta = 1$ (right) for different values of the coupling strength (solid lines - TDVP, dashed lines - TCL).