arXiv subjects

Friedemann Reinhard

Publications and source records attributed to Friedemann Reinhard.

25 records · Page 2Linked to original sources

arXiv2014

Tracking Temperature Dependent Relaxation Times of Individual Ferritin Nanomagnets with a Wide-band Quantum Spectrometer

We demonstrate the tracking of the spin dynamics of ensemble and individual magnetic ferritin proteins from cryogenic up to room temperature using the nitrogen-vacancy color center in diamond as magnetic sensor. We employ different detection protocols to probe the influence of the ferritin nanomagnets on the longitudinal and transverse relaxation of the nitrogen-vacancy center, which enables magnetic sensing over a wide frequency range from Hz to GHz. The temperature dependence of the observed spectral features can be well understood by the thermally induced magnetization reversals of the ferritin and enables the determination of the anisotropy barrier of single ferritin molecules.

cond-mat.mes-hall↗

arXiv2013

High-dynamic-range imaging of nanoscale magnetic fields using optimal control of a single qubit

We present a novel spectroscopy protocol based on optimal control of a single quantum system. It enables measurements with quantum-limited sensitivity (η_ω~ 1/sqrt(T_2^*),T_2^* denoting the system's coherence time) but has an orders of magnitude larger dynamic range than pulsed spectroscopy methods previously employed for this task. We employ this protocol to image nanoscale magnetic fields with a single scanning NV center in diamond. Here, our scheme enables quantitative imaging of a strongly inhomogeneous field in a single scan without closed-loop control, which has previously been necessary to achieve this goal.

quant-ph↗

arXiv2013

High-Resolution Correlation Spectroscopy of 13C Spins Near a Nitrogen-Vacancy Center in Diamond

Spin complexes comprising the nitrogen-vacancy (NV) center and neighboring spins are being considered as a building block for a new generation of spintronic and quantum information processing devices. Because assembling identical spin clusters is difficult, new strategies are in order to determine individual node structures with the highest precision. Here we use a pulse protocol to monitor the time evolution of the 13C ensemble in the vicinity of a NV center. We observe long-lived time correlations in the nuclear spin dynamics, limited by NV spin-lattice relaxation. We use the host 14N spin as a quantum register, and demonstrate that hyperfine-shifted resonances can be separated upon proper NV initialization. Intriguingly, we find that the amplitude of the correlation signal exhibits a sharp dependence on the applied magnetic field. We discuss this observation in the context of the quantum-to-classical transition proposed recently to explain the field dependence of the spin cluster dynamics.

cond-mat.mes-hall↗

arXiv2012

Augmenting the spin properties of shallow implanted NV-centers by CVD-overgrowth

The controlled scaling of diamond defect center based quantum registers relies on the ability to position NVs with high spatial resolution. Using ion implantation, shallow (< 10 nm) NVs can be placed with accuracy below 20nm, but generally show reduced spin properties compared to bulk NVs. We demonstrate the augmentation of spin properties for shallow implanted NV centers using an overgrowth technique. An increase of the coherence times up to an order of magnitude (T_2 = 250 μs) was achieved. Dynamic decoupling of defects spins achieves ms decoherence times. The study marks a further step towards achieving strong coupling among defects positioned with nm precision.

cond-mat.mtrl-sci↗

arXiv2011

Sensing electric fields using single diamond spins

The ability to sensitively detect charges under ambient conditions would be a fascinating new tool benefitting a wide range of researchers across disciplines. However, most current techniques are limited to low-temperature methods like single-electron transistors (SET), single-electron electrostatic force microscopy and scanning tunnelling microscopy. Here we open up a new quantum metrology technique demonstrating precision electric field measurement using a single nitrogen-vacancy defect centre(NV) spin in diamond. An AC electric field sensitivity reaching ~ 140V/cm/\surd Hz has been achieved. This corresponds to the electric field produced by a single elementary charge located at a distance of ~ 150 nm from our spin sensor with averaging for one second. By careful analysis of the electronic structure of the defect centre, we show how an applied magnetic field influences the electric field sensing properties. By this we demonstrate that diamond defect centre spins can be switched between electric and magnetic field sensing modes and identify suitable parameter ranges for both detector schemes. By combining magnetic and electric field sensitivity, nanoscale detection and ambient operation our study opens up new frontiers in imaging and sensing applications ranging from material science to bioimaging.

quant-ph↗

arXiv2010

Increasing the coherence time of single electron spins in diamond by high temperature annealing

Negatively charged Nitrogen-Vacancy (NV$^-$) centers in diamond produced by ion implantation often show properties different from NVs created during the crystal growth. We observe that NVs created from nitrogen ions with four different energies (30-300 keV) show much shorter electron spin coherence time $T_2$ compared to the "natural" NVs and we could find any dependence of $T_2$ on the implantation energy. Moreover, we also find out that about 10% of them show switching from NV$^-$to NV$^0$. We develop a method to increase $T_2$ of single NV$^-$ centers by annealing the sample at $t=1200 {\circ}$C whereas at the same time the fraction of the NVs showing discharging is greatly reduced.

cond-mat.mtrl-sci↗

arXiv2010

Spin self-rephasing and very long coherence times in a trapped atomic ensemble

We perform Ramsey spectroscopy on the ground state of ultra-cold 87Rb atoms magnetically trapped on a chip in the Knudsen regime. Field inhomogeneities over the sample should limit the 1/e contrast decay time to about 3 s, while decay times of 58 s are actually observed. We explain this surprising result by a spin self-rephasing mechanism induced by the identical spin rotation effect originating from particle indistinguishability. We propose a theory of this synchronization mechanism and obtain good agreement with the experimental observations. The effect is general and susceptible to appear in other physical systems.

quant-ph↗