[Paper Review] Floquet prethermalization with lifetime exceeding 90s in a bulk hyperpolarized solid

William Beatrez, Otto Janes+10 more|arXiv (Cornell University)|Apr 5, 2021

Atomic and Subatomic Physics Research59 references59 citations

TL;DR

This study demonstrates Floquet prethermalization in a bulk hyperpolarized 13C diamond solid at room temperature, achieving a transverse relaxation time T′₂ ≈ 90.9 seconds—over 60,000× longer than natural free induction decay (T₂* ≈ 1.5 ms). Using pulsed spin-lock driving and optical hyperpolarization via nitrogen-vacancy centers, the authors sustain a long-lived prethermal plateau through continuous spin interrogation over 573 seconds, enabling high-signal-to-noise observation of thermalization dynamics across four distinct regimes.

ABSTRACT

We report the observation of long-lived Floquet prethermal states in a bulk solid composed of dipolar-coupled $^{13}$C nuclei in diamond at room temperature. For precessing nuclear spins prepared in an initial transverse state, we demonstrate pulsed spin-lock Floquet control that prevents their decay over multiple-minute long periods. We observe Floquet prethermal lifetimes $T_2'\approx$90.9s, extended >60,000-fold over the nuclear free induction decay times. The spins themselves are continuously interrogated for $\sim$10min, corresponding to the application of $\approx$5.8M control pulses. The $^{13}$C nuclei are optically hyperpolarized by lattice Nitrogen Vacancy (NV) centers; the combination of hyperpolarization and continuous spin readout yields significant signal-to-noise in the measurements. This allows probing the Floquet thermalization dynamics with unprecedented clarity. We identify four characteristic regimes of the thermalization process, discerning short-time transient processes leading to the prethermal plateau, and long-time system heating towards infinite temperature. This work points to new opportunities possible via Floquet control in networks of dilute, randomly distributed, low-sensitivity nuclei. In particular, the combination of minutes-long prethermal lifetimes and continuous spin interrogation opens avenues for quantum sensors constructed from hyperpolarized Floquet prethermal nuclei.

Motivation & Objective

• To achieve and sustain long-lived prethermal states in a bulk, room-temperature solid with long coherence times.
• To overcome the intrinsic limitation of rapid spin decoherence in dipolar-coupled nuclear spin systems.
• To enable high-fidelity, continuous probing of non-equilibrium quantum dynamics in a driven many-body system.
• To explore the feasibility of using hyperpolarized, dilute, low-γ nuclei for robust quantum control and sensing applications.

Proposed method

• Employed pulsed spin-lock Floquet driving with periodic π/2 pulses at a repetition rate of ~10 kHz (τ ≈ 99.28 μs) to stabilize transverse nuclear spin coherence.
• Utilized optical hyperpolarization via nitrogen-vacancy (NV) centers to enhance 13C nuclear spin polarization by a factor of 223 over thermal equilibrium.
• Implemented continuous in-situ NMR readout with 1 ns temporal resolution, acquiring one data point per pulse cycle (tacq = 2–32 μs).
• Applied Fourier transformation to each acquisition window to extract the precession signal at the heterodyned frequency (20 MHz), forming the basis for decay curve reconstruction.
• Used moving average filtering (0.1 s window) to enhance signal-to-noise ratio and suppress high-frequency noise in the decay data.
• Varied the pulse flip angle (θ) and pulse spacing (τ) to probe the dependence of thermalization dynamics on drive parameters and system response.

Experimental results

Research questions

• RQ1 Can Floquet prethermalization be stabilized in a bulk, room-temperature solid of dilute, low-gyromagnetic ratio 13C nuclei with long-lived coherence?
• RQ2 What are the characteristic timescales and dynamical regimes of thermalization in a periodically driven, hyperpolarized spin system?
• RQ3 How does the signal-to-noise ratio enable the observation of transient dynamics and heating rates in the prethermal plateau and infinite-temperature regimes?
• RQ4 What is the scaling of heating rates with drive frequency, and does it follow theoretical predictions of exponential suppression?

Key findings

• A transverse relaxation time T′₂ ≈ 90.9 seconds was measured, representing a >60,000-fold extension over the natural free induction decay time T₂* ≈ 1.5 ms.
• The system remained in a stable prethermal plateau for over 573 seconds, corresponding to approximately 5.8 million control pulses and >10^10 spin precession cycles.
• Four distinct thermalization regimes were identified: (1) short-time transient to the prethermal plateau, (2) plateau maintenance, (3) crossover to unconstrained thermalization, and (4) eventual heating to infinite temperature.
• Heating rates scaled approximately as ∝ exp(−t^{1/2}) at high drive frequencies, consistent with theoretical predictions of suppressed energy absorption.
• The signal-to-noise ratio exceeded 10^9 per shot due to the combination of optical hyperpolarization and continuous readout, enabling high-fidelity tracking of dynamics.
• Harmonic oscillations in the transient response revealed coherent dynamics during the approach to the prethermal plateau, confirming the emergence of effective conserved quantities under periodic driving.