Spectral broadening and ultrafast dynamics of a nitrogen-vacancy center ensemble in diamond
At a Glance
Section titled āAt a Glanceā| Metadata | Details |
|---|---|
| Publication Date | 2021-03-29 |
| Journal | Materials for Quantum Technology |
| Authors | Albert Liu, Steven T. Cundiff, Diogo B. Almeida, Ronald Ulbricht |
| Institutions | University of Michigan, Universidade Estadual de Campinas (UNICAMP) |
| Citations | 34 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled āExecutive SummaryāThis research utilizes advanced ultrafast spectroscopy to characterize the fundamental decoherence mechanisms limiting the performance of nitrogen-vacancy (NV) center ensembles in bulk diamond, providing crucial data for quantum technology engineering.
- Decoherence Mechanism Identified: The dominant thermal dephasing mechanism is confirmed to be elastic interactions with a quasi-localized phonon mode, specifically a Jahn-Teller-induced vibronic state (Activation Energy Eph = 34.41 meV).
- Intrinsic Linewidth Quantified: The intrinsic, ensemble-averaged homogeneous linewidth is extremely broad, corresponding to a zero-temperature dephasing rate (Ī³0) of 37.31 GHz, yielding a very short coherence time (T2) of 26.8 ps.
- Ultrafast Spectral Diffusion: A second source of extrinsic broadeningāultrafast spectral diffusionāwas observed on the picosecond timescale (1.59 to 1.98 MHz/ps), occurring solely due to resonant photo-excitation.
- Stark Splitting Revealed: Multi-Dimensional Coherent Spectroscopy (MDCS) revealed a bimodal inhomogeneous distribution attributed to temperature-dependent Stark splitting (approx. 5 meV) of the excited orbital states, a feature invisible in standard linear absorption spectra.
- Engineering Insight: The results provide fundamental knowledge necessary for rationally engineering spectrally stable NV centers with narrow optical linewidths required for high-fidelity quantum applications.
Technical Specifications
Section titled āTechnical Specificationsā| Parameter | Value | Unit | Context |
|---|---|---|---|
| Sample Type | Type Ib Bulk Monocrystalline | N/A | Diamond host material used for NV center ensemble. |
| NV Density | 1-2 | ppm | Concentration of nitrogen-vacancy centers. |
| ZPL Center Energy | 1946 (637) | meV (nm) | Zero-Phonon Line (ZPL) transition energy. |
| Excitation Pulse Duration | 90 | fs | Duration of resonant laser pulses used for FWM/MDCS. |
| Laser Excitation Density | 1.0 | W/cm2 | Standard density used to ensure third-order nonlinear response. |
| Intrinsic Zero-Temp Dephasing Rate (Ī³0) | 37.31 | GHz | Extrapolated homogeneous linewidth at 0 K. |
| Intrinsic Zero-Temp Coherence Time (T2) | 26.8 | ps | Calculated coherence time (1/(ĻĪ³0)). |
| Activation Energy (Eph) | 34.41 | meV | Energy of the quasi-localized phonon mode causing thermal dephasing. |
| Ultrafast Spectral Diffusion Rate | 1.98 and 1.59 | MHz/ps | Measured linear increase rate of Ī³ vs. waiting time T (at 10 K). |
| Excited State Splitting (Observed) | Approx. 5 | meV (40 cm-1) | Bimodal inhomogeneous distribution attributed to Stark splitting. |
| Corresponding Internal Electric Field | 0.29 to 0.43 | MV/cm | Calculated field range corresponding to the observed splitting (50 K to 140 K). |
| Inhomogeneous Width (Ļ1) | 2.6 (627.8) | meV (GHz) | Width of the first Gaussian component of the bimodal distribution. |
Key Methodologies
Section titled āKey Methodologiesā- Sample Preparation: Type Ib bulk monocrystalline diamond was used. Vacancy centers were introduced via irradiation with 1 MeV electrons, followed by subsequent annealing, resulting in an NV density of 1-2 ppm.
- Cryogenic Environment: The sample was mounted to a cold-finger cryostat and cooled to cryogenic temperatures (measurements performed between 6 K and 140 K).
- Excitation Source: Three resonant laser pulses, approximately 90 fs in duration, were generated by an optical parametric amplifier operating at a 250 kHz repetition rate. The laser spectrum was centered on the NV- ZPL (1946 meV).
- Four-Wave Mixing (FWM) Setup: The three pulses (A, B, C) were focused onto the sample in a box geometry to generate a photon echo FWM signal.
- Detection: The FWM signal was heterodyne detected using a separate local-oscillator pulse routed around the sample.
- Multi-Dimensional Coherent Spectroscopy (MDCS): The FWM signal was recorded as a function of three time-delays (Ļ, T, and t). Fourier transforms along the absorption (Ļ) and emission (t) delays yielded the one-quantum spectrum, enabling unambiguous separation of homogeneous (Ī³) and inhomogeneous (Ļ) broadening.
- Spectral Diffusion Analysis: The homogeneous dephasing rate (Ī³) was measured as a function of the waiting time (T) between pulses B and C (from 1 ps to 2 ns) to quantify the rate of ultrafast spectral diffusion.
- Bimodal Fitting: Diagonal slices of the 2D spectra were modeled using two independent Gaussian distributions to extract the center frequencies (Ļ1 and Ļ2) of the excited orbital states as a function of temperature.
Commercial Applications
Section titled āCommercial ApplicationsāThe fundamental understanding of NV center decoherence mechanisms derived from this research is critical for advancing several quantum and high-tech industries:
- Quantum Computing and Memory: The short intrinsic coherence time (T2 = 26.8 ps) highlights the need for material engineering to suppress environmental interactions. This data guides efforts to create spectrally stable NV centers required for robust solid-state qubits and quantum entanglement protocols.
- Nanoscale Quantum Sensing: NV centers are premier sensors for electric fields, magnetic fields, and temperature. The observation of electric field-induced Stark splitting (0.29 to 0.43 MV/cm) provides the basis for developing new, microwave-free, all-optical electric-field sensing protocols in NV center ensembles.
- Single-Photon Emitters (Quantum Communication): Achieving spectrally narrow and stable optical linewidths is essential for high-fidelity single-photon sources. Mitigating the identified sources of broadening (phonon coupling and spectral diffusion) is necessary for integrating NV emitters into quantum communication networks.
- Advanced Diamond Material Manufacturing: The findings inform manufacturers (like those specializing in CVD diamond) about the required purity and strain control necessary during growth and post-processing (irradiation/annealing) to minimize the inhomogeneous broadening caused by local electric fields and strain.
View Original Abstract
Abstract Many applications of nitrogen-vacancy (NV) centers in diamond crucially rely on a spectrally narrow and stable optical zero-phonon line transition. Though many impressive proof-of-principle experiments have been demonstrated, much work remains in engineering NV centers with spectral properties that are sufficiently robust for practical implementation. To elucidate the mechanisms underlying their interactions with the environment, we apply multi-dimensional coherent spectroscopy to an NV center ensemble in bulk diamond at cryogenic temperatures. Our spectra reveal thermal dephasing due to quasi-localized vibrational modes as well as ultrafast spectral diffusion on the picosecond timescale. The intrinsic, ensemble-averaged homogeneous linewidth is found to be in the tens of GHz range by extrapolating to zero temperature. We also observe a temperature-dependent Stark splitting of the excited state manifold, relevant to NV sensing protocols.