[Paper Review] Solid-state platform for cooperative quantum dynamics driven by correlated emission

Xin Li, Jamir Marino+2 more|arXiv (Cornell University)|Sep 16, 2023

Neural Networks and Reservoir ComputingComputer Science3 citations

TL;DR

This paper proposes a solid-state platform using spin defects in a ferromagnetic reservoir to enable cooperative quantum dynamics via correlated dissipation. By leveraging magnon-mediated dissipative interactions, the authors demonstrate robust superradiance and subradiance in NV centers, even under spatial disorder and thermal fluctuations, establishing a foundation for scalable quantum technologies merging spintronics and quantum optics.

ABSTRACT

While traditionally regarded as an obstacle to quantum coherence, recent breakthroughs in quantum optics have shown that the dissipative interaction of a qubit with its environment can be leveraged to protect quantum states and synthesize many-body entanglement. Inspired by this progress, here we set the stage for the -- yet uncharted -- exploration of analogous cooperative phenomena in hybrid solid-state platforms. We develop a comprehensive formalism for the quantum many-body dynamics of an ensemble of solid-state spin defects interacting with the magnetic field fluctuations of a common solid-state reservoir. Our framework applies to any solid-state reservoir whose fluctuating spin, pseudospin, or charge degrees of freedom generate magnetic fields. To understand whether correlations induced by dissipative processes can play a relevant role in a realistic experimental setup, we apply our model to a qubit array interacting via the spin fluctuations of a ferromagnetic bath. Our results show that the low-temperature collective relaxation rates of the qubit ensemble can display clear signatures of super- and subradiance, i.e., forms of cooperative dynamics traditionally achieved in atomic ensembles. We find that the solid-state analog of these cooperative phenomena is robust against spatial disorder in the qubit ensemble and thermal fluctuations of the magnetic reservoir, providing a route for their feasibility in near-term experiments. Our work lays the foundation for a multi-qubit approach to quantum sensing of solid-state systems and the direct generation of many-body entanglement in spin-defect ensembles. Furthermore, we discuss how the tunability of solid-state reservoirs opens up novel pathways for exploring cooperative phenomena in regimes beyond the reach of conventional quantum optics setups.

Motivation & Objective

• To explore cooperative quantum phenomena in solid-state spin systems mediated by correlated dissipation via a common magnetic reservoir.
• To address the challenge of scalable two-qubit gates in quantum hybrid platforms where coherent coupling is limited by strong local dissipation.
• To investigate whether dissipative correlations—previously studied in photonic systems—can be harnessed in solid-state spin systems using magnons.
• To assess the robustness of cooperative quantum behavior against spatial disorder and thermal fluctuations in realistic experimental conditions.
• To lay the groundwork for merging spintronics and quantum optics by engineering long-range, dissipative correlations in solid-state platforms.

Proposed method

• Developed a general formalism for quantum many-body dynamics of spin defects interacting via magnetic field fluctuations of a shared solid-state reservoir.
• Formulated effective qubit-qubit interactions mediated by correlated dissipation, extending single-defect quantum sensing to nonlocal temporal and spatial correlation sensing.
• Applied the model to a system of NV centers coupled to a ferromagnetic thin film reservoir with tunable spin-wave dispersion and band gap.
• Used the Born-Markov approximation and the rotating wave approximation to derive a master equation describing collective relaxation dynamics.
• Simulated the time evolution of the density matrix under the master equation to analyze collective decay rates and second-order correlation functions.
• Incorporated finite-temperature effects by solving the master equation numerically at T = 100 mK to assess thermal robustness of quantum correlations.

Experimental results

Research questions

• RQ1 Can cooperative quantum dynamics such as superradiance and subradiance emerge in solid-state spin systems via correlated dissipation in a magnetic reservoir?
• RQ2 How do spatial disorder and thermal fluctuations affect the stability and observability of cooperative quantum states in such a platform?
• RQ3 To what extent can dissipative processes—typically detrimental—be harnessed to generate long-range entanglement and nonlocal correlations in spin qubit arrays?
• RQ4 What role do magnon-mediated dissipative interactions play in enabling non-unitary many-body dynamics beyond conventional photonic reservoirs?
• RQ5 Is the fermionization of subradiant two-excitation states a generic feature in dispersive many-body systems with structured baths?

Key findings

• Superradiant and subradiant collective relaxation rates emerge in an ensemble of NV centers coupled to a ferromagnetic reservoir when the spin-defect frequency exceeds the magnon band gap.
• The system exhibits clear signatures of cooperative dynamics, including enhanced (superradiant) and suppressed (subradiant) decay rates, in the appropriate parameter regime.
• Subradiant states display fermionic statistics in their two-excitation manifold, indicating a generic feature of dispersive many-body systems with structured baths.
• The cooperative quantum behavior remains robust against spatial disorder in the positions of the spin defects, indicating resilience to experimental imperfections.
• Thermal fluctuations at T = 100 mK disrupt fermionic correlations in multi-excited states, as evidenced by the decay of second-order correlation functions over time.
• The framework enables nonlocal sensing of temporal and spatial correlations in magnetic noise, extending the scope of quantum sensing beyond single-defect measurements.