Non-classical photon-phonon correlations at room temperature
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2021-01-01 |
| Journal | Infoscience (Ecole Polytechnique Fédérale de Lausanne) |
| Authors | Santiago Tarrago Velez |
| Analysis | Full AI Review Included |
Technical Documentation & Analysis: MPCVD Diamond for Room-Temperature Quantum Phononics
Section titled âTechnical Documentation & Analysis: MPCVD Diamond for Room-Temperature Quantum PhononicsâThis document analyzes the attached research thesis, âNon-classical photon-phonon correlations at room temperature,â focusing on the experimental requirements and achievements related to MPCVD diamond, and directly linking them to 6CCVDâs advanced material capabilities.
Executive Summary
Section titled âExecutive SummaryâThe research successfully demonstrates the creation, manipulation, and measurement of non-classical phonon states in bulk materials at ambient conditions, leveraging the unique properties of diamond.
- Room-Temperature Quantum Memory: Achieved preparation and measurement of the single quantum of vibration ($n=1$ Fock state) in diamondâs optical phonon mode (39.9 THz) at room temperature.
- High-Fidelity State Preparation: Demonstrated $98.5%$ probability of preparing the vibrational mode in the $n=1$ Fock state upon heralding a Stokes photon.
- Bell Correlation Violation: Experimentally verified strong photon-phonon entanglement by violating the CHSH Bell inequality, measuring $S = 2.360 \pm 0.025$.
- Phonon Dynamics: Measured the optical phonon lifetime in diamond to be $3.9 \pm 0.7$ ps, confirming its viability as an ultrafast quantum memory resource.
- Novel Methodology: Introduced a two-color pump-probe scheme combined with Time Correlated Single Photon Counting (TCSPC) to circumvent polarization limitations, making the technique broadly applicable to various Raman-active materials.
- Material Requirement: Success relies critically on the high purity and low defect density of the synthetic diamond crystal used as the quantum medium.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Primary Material | Synthetic Diamond Crystal | N/A | Used for Fock state preparation and Bell tests |
| Crystal Orientation | (100) | N/A | Sample cut axis |
| Sample Thickness | $\sim 300$ | ”m | Used in transmission geometry |
| Optical Phonon Frequency ($\Omega_m/2\pi$) | 39.9 | THz | Vibrational mode used for quantum memory |
| Phonon Lifetime ($\tau_m$) | $3.9 \pm 0.7$ | ps | Measured decay time of the single phonon Fock state |
| CHSH Parameter (S) | $2.360 \pm 0.025$ | N/A | Violates classical bound (S $\le$ 2) |
| Heralded Fock State Purity | 98.5 | % | Probability of preparing the $ |
| Operating Conditions | Room Temperature | K | Ambient conditions |
| Laser Repetition Rate | 80 | MHz | Used for synchronized pulse trains |
| Laser Pulse Duration | $\sim 100$ to 200 | fs | Ultrafast excitation pulses |
| Stokes-anti-Stokes Correlation ($g^{(2)}_{S,aS}(0)$) | $63.4 \pm 9.7$ | N/A | Measured non-classical correlation at zero delay |
Key Methodologies
Section titled âKey MethodologiesâThe experimental success hinges on combining ultrafast optics with quantum correlation measurements, specifically tailored to isolate and measure single phonon quanta.
- Two-Color Pump-Probe Excitation: Utilizes two synchronized femtosecond laser pulses (Write pulse $\omega_1$, Read pulse $\omega_2$) tuned such that the Stokes and anti-Stokes signals are spectrally separated, enabling signal distinction via frequency filtering rather than polarization rules.
- Spontaneous Raman Scattering (Write Operation): The Write pulse probabilistically generates a Stokes photon and a phonon (vibrational quantum). Detection of the Stokes photon acts as a âherald,â projecting the phonon mode into the non-classical $n=1$ Fock state.
- Anti-Stokes Readout (Read Operation): After a variable time delay ($\Delta t$), the Read pulse interacts with the prepared phonon state, converting the phonon back into an anti-Stokes photon, thereby reading out the vibrational state population.
- Time Correlated Single Photon Counting (TCSPC): Used to measure the second-order cross-correlation function ($g^{(2)}_{S,aS}(\Delta t)$) between the heralded Stokes photon and the anti-Stokes readout photon, revealing the phonon lifetime and non-classicality.
- Bell Correlation Measurement: Time-bin entanglement is mapped onto polarization qubits using an unbalanced Mach-Zehnder interferometer, allowing the measurement of the CHSH parameter to quantify the strength of the photon-phonon entanglement.
6CCVD Solutions & Capabilities
Section titled â6CCVD Solutions & CapabilitiesâThe groundbreaking results achieved in room-temperature quantum phononics rely on materials with exceptional purity and crystalline quality. 6CCVD is uniquely positioned to supply and engineer the diamond substrates required to replicate and advance this research.
Applicable Materials
Section titled âApplicable MaterialsâThe core requirement is a material that minimizes thermal occupancy and maximizes coherence time.
- Optical Grade Single Crystal Diamond (SCD): This material is essential for replicating the high-fidelity Fock state preparation and Bell correlation violation.
- Purity: SCD minimizes defects and nitrogen content, which are critical for maintaining the long coherence time of the optical phonon mode (39.9 THz).
- Thermal Management: The high thermal conductivity of SCD ensures stable operation, crucial for maintaining the precise temporal and spatial overlap required by the pump-probe scheme.
Customization Potential for Quantum Research
Section titled âCustomization Potential for Quantum Researchâ6CCVDâs MPCVD capabilities directly address the needs for advanced quantum experiments, particularly those involving integration and scaling.
| Requirement from Research | 6CCVD Capability | Technical Advantage |
|---|---|---|
| Crystallographic Orientation | Custom SCD plates cut along (100), (111), or (110) axes. | Ensures optimal alignment for Raman scattering geometry and specific polarization selection rules (if required). |
| Thickness Control | SCD plates available from $0.1$ ”m up to $500$ ”m. | Allows researchers to optimize interaction length for pulsed experiments or integrate thin membranes into micro-cavities (Ch. 8). |
| Surface Quality | Ultra-low roughness polishing (Ra < 1 nm for SCD). | Minimizes scattering losses, crucial for high-NA objective coupling (NA=0.8 used in the study) and integration into resonant structures. |
| Advanced Integration | In-house metalization services (Au, Pt, Ti, W, Cu). | Enables fabrication of on-chip plasmonic or electrical structures directly onto the diamond surface for enhanced light-matter coupling (as suggested in Ch. 8). |
| Scaling & Geometry | Custom dimensions and precision laser cutting services. | Supports the development of large-scale quantum memory arrays or complex device geometries. |
Engineering Support
Section titled âEngineering Supportâ6CCVDâs in-house PhD team specializes in the material science of diamond for quantum applications. We offer consultation services to assist researchers in optimizing material specifications (purity, orientation, and surface preparation) for Ultrafast Quantum Optics and Phonon Memory projects.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
With the development of quantum optics, photon correlations acquired a prominent role as a tool to test our understanding of physics, and played a key role in verifying the validity of quantum mechanics. The spatial and temporal correlations in a light field also reveal information about its origin, and allow us to probe the nature of the physical systems interacting with it. Additionally, with the advent of quantum technologies, they have acquired technological relevance, as they are expected to play an important role in quantum communication and quantum information processing. This thesis develops techniques that combine spontaneous Raman scattering with Time Correlated Single Photon Counting, and uses them to study the quantum mechanical nature of high frequency vibrations in crystals and molecules. We demonstrate photon bunching in the Stokes and anti-Stokes fields scattered from two ultrafast laser pulses, and use their cross-correlation to measure the 3.9 ps decay time of the optical phonon in diamond. We then employ this method to measure molecular vibrations in CS2, where we are able to excite the respective vibrational modes of the two isotopic species present in the sample in a coherent superposition, and observe quantum beating between the two signals. Stokes scattering, when combined with a projective measurement, leads to a well defined quantum state. We demonstrate this by measuring the second order correlation function of the anti-Stokes field conditional on detecting one or more photons in the Stokes field, which allows us to observe a phonon modeĂą s transition form a thermal state into the first excited Fock state, and measure its decay over the characteristic phonon lifetime. Finally, we use this technique to prepare a highly entangled photon-phonon state, which violates a Bell-type inequality. We measure S = 2.360 ñ 0.025, violating the CHSH inequality, compatible with the non-locality of the state. The techniques we developed open the door to the study of a broad range of physical systems, where spectroscopic information is obtained with the preparation of specific quantum states. They also hold potential for future technological use, and promote vibrational Raman scattering to a resource in nonlinear quantum optics â where it used to be considered as a source of noise instead.