Density and 
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 of Surface and Bulk Spins in Diamond in High Magnetic Field Gradients

Surfaces enable useful functionalities for quantum systems, e.g. as interfaces to sensing targets, but often result in surface-induced decoherence where unpaired electron spins are common culprits. Here we show that the coherence time of a near-surface qubit is increased by coherent radio-frequency driving of surface electron spins, where we use a diamond nitrogen-vacancy (NV) center as a model qubit. This technique is complementary to other methods of suppressing decoherence, and importantly, requires no additional materials processing or control of the qubit. Further, by combining driving with the increased magnetic susceptibility of the double-quantum basis we realize an overall fivefold sensitivity enhancement in NV magnetometry. Informed by our results, we discuss a path toward relaxation-limited coherence times for near-surface NV centers. The surface spin driving technique presented here is broadly applicable to a wide variety of qubit platforms afflicted by surface-induced decoherence. arXiv:1905.06405v1 [quant-ph]

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“…The bounded range of 0.01 − 0.1/nm 2 is consistent with the densities extracted by various different methods in Refs. [6,49,64].…”

Section: Supplemental Note 2: Surface Spin Density Estimatementioning

confidence: 99%

Extending the Quantum Coherence of a Near-Surface Qubit by Coherently Driving the Paramagnetic Surface Environment

et al. 2019

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“…A diamond of 230 nm radius contains ∼ 10 9 carbon atoms, which indicates that even for 13 C concentrations as low as 10 −6 % the diamond will contain ∼ 10 3 nuclear spins. On the other hand, the most optimistic estimates for the dangling bond density on the surface of diamond are on the order of 10 −2 dangling bonds per nm 2 (estimated for single crystal bulk diamond grown under optimal conditions) [49], which amounts to a total of 10 3 electron spins on a 230 nm diamond. All in all, one could expect that such a diamond will have a magnetic moment of…”

Section: Constant Homogeneous Forcesmentioning

confidence: 99%

Motional Dynamical Decoupling for Matter-Wave Interferometry

Pedernales,

Morley,

Plenio

2019

Preprint

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Matter-wave interferometry provides a remarkably sensitive tool for probing minute forces and, potentially, the foundations of quantum physics by making use of interference between spatially separated matter waves. Furthering this development requires ever-increasing stability of the interferometer, typically achieved by improving its physical isolation from the environment. Here we introduce as an alternative strategy the concept of dynamical decoupling applied to spatial degrees of freedom of massive objects. We show that the superposed matter waves can be driven along paths in space that render their superposition resilient to many important sources of noise. As a concrete implementation, we present the case of matter-wave interferometers in a magnetic field gradient based on either levitated or free-falling nanodiamonds hosting a color center. We present an in-depth analysis of potential sources of decoherence in such a setup and of the ability of our protocol to suppress them. These effects include gravitational forces, interactions of the net magnetic and dipole moments of the diamond with magnetic and electric fields, surface dangling bonds, rotational degrees of freedom, Casimir-Polder forces, and diamagnetic forces. Contrary to previous analyses, diamagnetic forces are not negligible in this type of interferometers and, if not acted upon lead to small separation distances that scale with the inverse of the magnetic field gradient. We show that our motional dynamical decoupling strategy renders the system immune to such limitations while continuing to protect its coherence from environmental influences, achieving a linear-in-time growth of the separation distance independent of the magnetic field gradient. Hence, motional dynamical decoupling may become an essential tool in driving the sensitivity of matter-wave interferometry to the next level.

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Magnetic Cooling and Vibration Isolation of a Sub-kHz Mechanical Resonator

Heck

Fuchs²,

Jaimy³

et al. 2023

J Low Temp Phys

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We report recent progress toward the realization of a sub-mK, low-vibration environment at the bottom stage of a dry dilution refrigerator for use in mechanical tests of quantum mechanics. Using adiabatic nuclear demagnetization, we have cooled a silicon cantilever force sensor to $$T\approx 1$$ T ≈ 1 mK. The temperature of the tip holder of the cantilever chip was determined via a primary magnetic flux noise thermometer. The quality factor of the cantilever continues to increase with decreasing temperature, reaching $$Q\approx 4\cdot 10^4$$ Q ≈ 4 · 10 4 at 2 mK. To demonstrate that the vibration isolation is not compromised, we report the detection of the thermal motion of the cantilever down to $$T \approx 20$$ T ≈ 20 mK, only limited by the coupling to the SQUID readout circuit. We discuss feasible improvements that will allow us to probe unexplored regions of the parameter space of continuous spontaneous localization models.

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Density and T1 of Surface and Bulk Spins in Diamond in High Magnetic Field Gradients

Cited by 6 publications

References 30 publications

Extending the Quantum Coherence of a Near-Surface Qubit by Coherently Driving the Paramagnetic Surface Environment

Extending the Quantum Coherence of a Near-Surface Qubit by Coherently Driving the Paramagnetic Surface Environment

Motional Dynamical Decoupling for Matter-Wave Interferometry

Magnetic Cooling and Vibration Isolation of a Sub-kHz Mechanical Resonator

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