Experimental signature of initial quantum coherence on entropy production
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2023-09-11 |
| Journal | npj Quantum Information |
| Authors | Santiago HernĂĄndez-GĂłmez, Stefano Gherardini, Alessio Belenchia, Andrea Trombettoni, Mauro Paternostro |
| Institutions | University of TĂŒbingen, University of Trieste |
| Citations | 16 |
| Analysis | Full AI Review Included |
Technical Documentation: Quantum Coherence and Entropy Production in NV Diamond
Section titled âTechnical Documentation: Quantum Coherence and Entropy Production in NV DiamondâSource Paper: HernĂĄndez-GĂłmez et al., âExperimental signature of initial quantum coherence on entropy production,â npj Quantum Information (2023) 9:86.
Executive Summary
Section titled âExecutive SummaryâThis research successfully quantifies the contribution of initial quantum coherence to non-equilibrium entropy production using a Nitrogen-Vacancy (NV) center spin qubit in diamond. The findings validate the End-Point Measurement (EPM) approach as a powerful tool for quantum thermodynamics in open systems.
- Platform: Qubit encoded in the electronic spin (S=1) of an NV defect in a solid-state diamond lattice.
- Methodology: Utilized the EPM scheme, which preserves initial quantum coherence, unlike the traditional Two-Point Measurement (TPM) scheme.
- Key Achievement: Experimentally demonstrated that initial quantum coherence ($\chi$) significantly increases the irreversible entropy production ($\Delta\Sigma$) of the dissipative map.
- Fluctuation Theorem Verification: Verified the integral fluctuation theorem for the coherence-affected entropy production, showing $\langle e^{-\Delta\Sigma} \rangle_{\Gamma} = 1$, with experimental values tightly clustered in the range [0.97, 1.03].
- System Dynamics: The NV center was subjected to controlled dissipative dynamics via a sequence of coherent microwave driving and short laser pulses (optical pumping).
- 6CCVD Relevance: The success of this experiment relies entirely on high-quality, high-purity Single Crystal Diamond (SCD) substrates, a core offering of 6CCVD, essential for maintaining long NV spin coherence times.
Technical Specifications
Section titled âTechnical SpecificationsâThe following table summarizes the key experimental parameters and results extracted from the research paper, focusing on the NV-diamond platform and thermodynamic quantification.
| Parameter | Value | Unit | Context |
|---|---|---|---|
| Material Platform | NV Center in Diamond | N/A | Electronic spin S=1 qubit |
| System Temperature | Room Temperature | °C | Solid-state platform operation |
| Qubit Basis | $ | S_z = 0\rangle \leftrightarrow | S_z = +1\rangle$ |
| Pulse Duration ($t_l$) | 190 | ns | Short laser pulse (dissipative channel) |
| Driving Condition ($\alpha$) | $\pi/4$ | Radians | Set by $\delta = -\Omega$ (Detuning = -Rabi Frequency) |
| Time Interval ($\tau\omega$) | $\sim (2\pi)0.9$ | N/A | Between consecutive pulses |
| Measurement Scheme | End-Point Measurement (EPM) | N/A | Single final energy measurement |
| Measurement Repetitions | $\sim 10^{6}$ | N/A | For PL intensity readout (normalized signal $s$) |
| Fluctuation Theorem Verification | $\langle e^{-\Delta\Sigma} \rangle_{\Gamma}$ | N/A | Verified in the range [0.97, 1.03] |
| Coherence Contribution ($\langle\Delta\Sigma\rangle$) | Positive (up to 0.05) | N/A | Increases with number of pulses (N) |
| Polishing Requirement | Ultra-high quality | N/A | Essential for minimizing surface defects and maximizing NV coherence |
Key Methodologies
Section titled âKey MethodologiesâThe experiment utilized a highly controlled open quantum system protocol implemented on the NV center spin qubit.
- Initialization: The electronic spin was initialized into the $|S_z = 0\rangle$ eigenstate via optical spin pumping using long laser excitation.
- Initial State Preparation: Rotation gates (on-resonant microwave pulses) were applied to prepare the system in one of four pure states (eigenvectors of $\sigma_z$ and $\sigma_y$), including states exhibiting initial quantum coherence ($\chi$).
- Controlled Dynamics: The qubit was subjected to an alternating sequence of unitary and non-unitary dynamics over $N$ pulses:
- Unitary Evolution: Described by $U = \exp[-iHt]$ between pulses (coherent driving via continuous microwave field).
- Dissipative Evolution: Induced by a train of short laser pulses ($t_l = 190$ ns), acting as a controlled dissipative channel (optical pumping toward $|S_z = 0\rangle$).
- End-Point Measurement (EPM): After $N$ pulses, the final energy of the system was measured in the Hamiltonian basis ($\tilde{\sigma}_z$) using optical readout of the NV photo-luminescence (PL) intensity.
- Data Analysis: The EPM probability distribution $P_{\text{EPM}}(\Delta E)$ was computed from the PL readout statistics, allowing for the quantification and averaging of the coherence-affected irreversible entropy production $\Delta\Sigma_{i,f}$.
6CCVD Solutions & Capabilities
Section titled â6CCVD Solutions & CapabilitiesâThe successful replication and extension of this groundbreaking quantum thermodynamics research requires diamond materials with exceptional purity, crystal quality, and precise surface engineeringâall core competencies of 6CCVD.
Applicable Materials
Section titled âApplicable MaterialsâTo achieve the high spin coherence and optical control necessary for NV center experiments, the following 6CCVD material is required:
- Optical Grade Single Crystal Diamond (SCD):
- Requirement Match: The experiment demands extremely low background nitrogen and high crystalline perfection to ensure long coherence times ($T_2$) for the NV centers. Our Optical Grade SCD is grown via MPCVD to minimize impurities and defects, providing the ideal host lattice.
- Thickness Control: We offer SCD plates with thicknesses ranging from 0.1”m up to 500”m, allowing researchers to select the optimal thickness for NV implantation depth, waveguide integration, or bulk studies.
Customization Potential
Section titled âCustomization PotentialâThe integration of NV centers into complex quantum devices often necessitates specific geometries and surface treatments. 6CCVD provides comprehensive customization services to meet these needs:
| Research Requirement | 6CCVD Customization Capability | Benefit to Researcher |
|---|---|---|
| Specific Dimensions | Plates/wafers up to 125mm (PCD) and custom SCD sizes. | Provides large-area substrates for scaling up quantum circuits or fabricating multiple devices. |
| Surface Quality | Ultra-low roughness polishing: Ra < 1nm (SCD). | Minimizes surface defects and phonon scattering, which are critical for preserving NV spin coherence and optical properties. |
| Microwave Delivery | Custom Metalization services (Au, Pt, Pd, Ti, W, Cu). | Enables the fabrication of on-chip microwave structures (e.g., coplanar waveguides) directly on the diamond surface for coherent driving (as used in this paper). |
| Device Integration | Precision laser cutting and shaping services. | Allows for the creation of specific geometries (e.g., micro-pillars, resonators) required for enhanced light collection or integration into cryogenic systems. |
Engineering Support
Section titled âEngineering SupportâThe theoretical framework utilized (EPM-based fluctuation theorem) is highly complex, requiring precise material properties to validate. 6CCVDâs in-house team of PhD material scientists and engineers specializes in diamond for quantum applications.
- Expert Consultation: Our team can assist researchers in selecting the optimal SCD grade, nitrogen concentration (if intentional NV creation is desired), and surface orientation for similar Quantum Thermodynamics or Quantum Sensing projects.
- Global Logistics: We ensure reliable, global delivery of sensitive materials, offering DDU (default) and DDP shipping options worldwide.
Call to Action: For custom specifications or material consultation tailored to your quantum coherence or NV center project, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
Abstract We report on the experimental quantification of the contribution to non-equilibrium entropy production stemming from the quantum coherence content in the initial state of a qubit exposed to both coherent driving and dissipation. Our experimental demonstration builds on the exquisite experimental control of the spin state of a nitrogen-vacancy defect in diamond and is underpinned, theoretically, by the formulation of a generalized fluctuation theorem designed to track the effects of quantum coherence. Our results provide significant evidence of the possibility to pinpoint the genuinely quantum mechanical contributions to the thermodynamics of non-equilibrium quantum processes in an open quantum systems scenario.