Dynamical Decoupling of a single electron spin at room temperature (1008.1953v2)

Abstract: Here we report the increase of the coherence time T$_2$ of a single electron spin at room temperature by using dynamical decoupling. We show that the Carr-Purcell-Meiboom-Gill (CPMG) pulse sequence can prolong the T$_2$ of a single Nitrogen-Vacancy center in diamond up to 2.44 ms compared to the Hahn echo measurement where T$_2 = 390 \mu$s. Moreover, by performing spin locking experiments we demonstrate that with CPMG the maximum possible $T_2$ is reached. On the other hand, we do not observe strong increase of the coherence time in nanodiamonds, possibly due to the short spin lattice relaxation time $T_1=100 \mu$s (compared to T$_1$ = 5.93 ms in bulk). An application for detecting low magnetic field is demonstrated, where we show that the sensitivity using the CPMG method is improved by about a factor of two compared to the Hahn echo method.

• The paper demonstrates that applying the CPMG pulse sequence boosts NV center electron spin coherence from 390µs to 2.44ms, a six-fold improvement over the Hahn echo method.
• The experimental approach adapts advanced dynamical decoupling from NMR to ESR contexts, effectively maintaining quantum coherence at room temperature.
• The findings imply that extended coherence enhances quantum sensing sensitivity by nearly two times, paving the way for more robust quantum computing and magnetometry applications.

Dynamical Decoupling of a Single Electron Spin at Room Temperature

The paper "Dynamical Decoupling of a Single Electron Spin at Room Temperature" by Naydenov et al. explores the enhancement of coherence times for a single electron spin in nitrogen-vacancy (NV) centers in diamond at room temperature through the application of the Carr-Purcell-Meiboom-Gill (CPMG) pulse sequence. This study is poised within the broader context of quantum computing and magnetometry where long coherence times are desirable for the practical implementation of quantum systems.

Researchers have long been interested in NV centers due to their remarkably long coherence times under ambient conditions. Previous techniques have achieved coherence times $T_2$ up to nearly 2 milliseconds in ultra-pure environments. However, this work addresses the challenges of maintaining quantum coherence in less controlled settings by extending $T_2$ using CPMG sequences, a method carried over from Nuclear Magnetic Resonance (NMR).

Experimental Findings and Results

The authors demonstrate that by employing the CPMG pulse sequence, the coherence time $T_2$ of a single NV center can be significantly extended from 390 microseconds, obtained using a Hahn echo technique, to as long as 2.44 milliseconds. This is particularly noteworthy because the CPMG sequence has traditionally found limited application in Electron Spin Resonance (ESR) contexts.

Key numerical results of the study include:

• An enhancement factor of six in coherence time with CPMG compared to the Hahn echo sequence.
• A spin locking experiment confirming that further increase in coherence time is confined by the spin-lattice relaxation time $T_1$, which they measured as 5.93 milliseconds for bulk diamond.

Contrastingly, in nanodiamonds, known for their shorter spin-lattice relaxation times due to environmental factors, the same CPMG sequence yielded less pronounced improvements — a doubling of $T_2$ from 2.1 microseconds to 4.8 microseconds.

Implications and Future Directions

The implications for quantum computing and magnetometry are substantial. The extended $T_2$ achieved via the CPMG sequence directly correlates with an enhancement of the signal-to-noise ratio in quantum sensing applications, such as the detection of low-frequency magnetic fields. The researchers report an improvement in sensitivity by approximately a factor of two using CPMG over the Hahn echo method — a critical advance for applications requiring precise magnetic field measurements at nanoscale levels.

Future explorations may focus on optimizing dynamical decoupling sequences further, especially in environments with less pure diamond samples or other solid-state systems with similarly promising quantum properties. Moreover, understanding the interactions at play in nanodiamond samples could reveal additional steps necessary to overcome environmental noise.

This research advances theoretical and practical understanding of quantum coherence, pushing the bounds of quantum information science towards more robust and sensitive applications in ambient conditions. Continuing research on dynamical decoupling in other quantum systems could potentially lead to universally applicable techniques that allow for even greater coherence times and more precise quantum measurements across a broader range of materials.