Quantum control and Berry phase of electron spins in rotating levitated diamonds in high vacuum
At a Glance
Section titled “At a Glance”| Metadata | Details |
|---|---|
| Publication Date | 2024-06-13 |
| Journal | Nature Communications |
| Authors | Yuanbin Jin, Kunhong Shen, Peng Ju, Xingyu Gao, Chong Zu |
| Institutions | Purdue University West Lafayette, Sandia National Laboratories |
| Citations | 19 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled “Executive Summary”This research demonstrates a breakthrough in interfacing mechanical rotation with spin qubits by achieving stable levitation and ultra-fast rotation of nanodiamonds (NDs) in high vacuum (HV).
- High-Vacuum Levitation: Stable levitation of NDs was achieved in a surface ion trap at pressures below 10-5 Torr, overcoming previous limitations where diamonds were lost above 0.01 Torr.
- Thermal Stability: The internal temperature of the levitated ND remains stable at approximately 350 K in HV (below 5 x 10-5 Torr), suitable for maintaining NV spin quantum coherence.
- Ultra-Fast Rotation: The NDs were driven to rotate up to 20 MHz (1.2 x 109 rpm), a speed three orders of magnitude faster than previous motor-mounted systems, and crucially, faster than the typical NV spin dephasing rate.
- Quantum Geometric Phase: The effect of the Berry phase (quantum geometric phase) generated by the mechanical rotation was successfully observed using the embedded NV electron spins.
- Spin Control in Motion: Quantum control (Rabi oscillations) of NV centers was demonstrated within the fast-rotating nanodiamond, requiring synchronization between the microwave pulse and the particle’s rotation phase.
- Center-of-Mass (CoM) Cooling: Feedback cooling was implemented, reducing the CoM motion temperature to a minimum of 1.2 K along the x-direction, paving the way for quantum spin-mechanics studies.
Technical Specifications
Section titled “Technical Specifications”| Parameter | Value | Unit | Context |
|---|---|---|---|
| Minimum Levitation Pressure | 6.9 x 10-6 | Torr | Stable ODMR measurement pressure |
| Internal Temperature (Stable) | ~350 | K | Stable below 5 x 10-5 Torr |
| Maximum Rotation Frequency | 20 | MHz | 1.2 x 109 rpm |
| Nanodiamond Radius | ~264 | nm | Estimated from CoM motion PSDs |
| CoM Temperature (X-axis, Cooled) | 1.2 ± 0.3 | K | Achieved via feedback cooling (FB) |
| CoM Temperature (Y-axis, Cooled) | 3.5 ± 0.4 | K | Achieved via feedback cooling (FB) |
| CoM Temperature (Z-axis, Cooled) | 86 ± 26 | K | Achieved via feedback cooling (FB) |
| NV Spin Relaxation Time (T1) | ~3.6 | ms | Levitated nanodiamond |
| NV Spin Initialization Time | 1.05 | ms | At 532 nm laser intensity of 0.113 W/mm2 |
| Excitation Laser Intensity (532 nm) | 0.030 | W/mm2 | For ODMR measurements |
| Microwave Antenna Angle (θ’) | 8.5 | ° | Angle relative to z-axis |
| Ion Trap AC Voltage | 200 | V | Applied at 20 kHz frequency |
| Nanodiamond Charge (Q) | > 1000 | e | Elementary charges (e) |
Key Methodologies
Section titled “Key Methodologies”The experiment relies on an integrated surface ion trap and advanced optical/microwave control systems:
- Integrated Surface Ion Trap Fabrication: A surface ion trap was fabricated on a sapphire wafer, chosen for its high optical transmittance, enabling simultaneous levitation and optical access for spin control. The trap incorporates a Q-shaped stripline for combined low-frequency high voltage (HV) trapping and high-frequency microwave (MW) delivery.
- Particle Charging and Delivery: Nanodiamonds (NDs) containing NV centers were charged (typically > 1000 e) using electrospray and delivered to the surface trap via an auxiliary linear Paul trap.
- Levitation and Stabilization: Levitation was achieved by applying 20 kHz, 200 V AC high voltage. Four corner electrodes were used with compensation DC voltages to minimize micro-motion and stabilize the trap center, located 253 µm above the chip surface.
- Internal Thermometry (ODMR): The internal temperature of the levitated ND was measured using NV centers as thermometers. The zero-field splitting (D) of the NV spin resonance, measured via ODMR, is correlated with temperature (D = C0 + C1T + C2T2 + C3T3 + Apressure + Astrain).
- Fast Rotation Drive: A rotating electric field was generated by applying AC voltage signals (A sin(ωt + φ)) with π/2 phase differences between neighboring electrodes. The resulting torque drives the charged ND to rotate, achieving frequencies up to 20 MHz.
- Berry Phase Measurement: An external static magnetic field (100 G along the z-axis) was applied to separate the NV energy levels. The frequency shift of the spin resonance (D ± gµBB cos θ ± ωr cos θ) was measured as a function of rotation frequency (ωr), isolating the Berry phase contribution (±ωr cos θ).
- Quantum Control Synchronization: Rabi oscillation measurements were performed by synchronizing the microwave pulse timing with the rotation phase (φ) of the ND, ensuring the microwave magnetic field projection along the NV axis was controlled during the pulse.
- Center-of-Mass (CoM) Feedback Cooling: CoM motion signals were read out, and a π/2 phase delay was applied to obtain velocity signals. An FPGA-based feedback loop then applied electric forces proportional to and opposite the velocity, cooling the CoM motion to near the quantum ground state (1.2 K minimum).
Commercial Applications
Section titled “Commercial Applications”This technology, based on levitated nanodiamonds and NV spin qubits, is highly relevant to several high-precision engineering and quantum technology fields:
- Quantum Sensing and Metrology:
- Sensitive Gyroscopes: The observed Berry phase and spin-rotation coupling enable the development of highly sensitive gyroscopes (rotational sensors) that utilize the NV nuclear or electron spin.
- AC Magnetometry: The rotating NV centers experience an AC magnetic field, which can be leveraged for high-sensitivity AC magnetic field sensing, surpassing DC magnetic field sensitivity limits.
- Fundamental Physics and Gravity:
- Quantum Gravity Tests: The platform is proposed for creating massive quantum superpositions (NDs are massive objects) to test the limits of quantum mechanics and quantum gravity theories.
- Rotational Interferometry: Building rotational matter-wave interferometers for precision tests of inertia and rotational dynamics.
- Quantum Information Processing:
- Isolated Qubit Platforms: The high isolation achieved in high vacuum makes the levitated ND an ideal platform for studying and controlling quantum states, potentially leading to new architectures for quantum computing and simulation.
- High-Vacuum Instrumentation:
- Precision Measurement in UHV: The demonstrated stability of the ion trap and internal temperature in high vacuum (below 10-5 Torr) validates the use of this system for other precision measurements requiring ultra-clean, isolated environments.