202 research outputs found
Observation of anomalous decoherence effect in a quantum bath at room temperature
Decoherence of quantum objects is critical to modern quantum sciences and
technologies. It is generally believed that stronger noises cause faster
decoherence. Strikingly, recent theoretical research discovers the opposite
case for spins in quantum baths. Here we report experimental observation of the
anomalous decoherence effect for the electron spin-1 of a nitrogen-vacancy
centre in high-purity diamond at room temperature. We demonstrate that under
dynamical decoupling, the double-transition can have longer coherence time than
the single-transition, even though the former couples to the nuclear spin bath
as twice strongly as the latter does. The excellent agreement between the
experimental and the theoretical results confirms the controllability of the
weakly coupled nuclear spins in the bath, which is useful in quantum
information processing and quantum metrology.Comment: 22 pages, related paper at http://arxiv.org/abs/1102.557
Composite-pulse magnetometry with a solid-state quantum sensor
The sensitivity of quantum magnetometers is challenged by control errors and,
especially in the solid-state, by their short coherence times. Refocusing
techniques can overcome these limitations and improve the sensitivity to
periodic fields, but they come at the cost of reduced bandwidth and cannot be
applied to sense static (DC) or aperiodic fields. Here we experimentally
demonstrate that continuous driving of the sensor spin by a composite pulse
known as rotary-echo (RE) yields a flexible magnetometry scheme, mitigating
both driving power imperfections and decoherence. A suitable choice of RE
parameters compensates for different scenarios of noise strength and origin.
The method can be applied to nanoscale sensing in variable environments or to
realize noise spectroscopy. In a room-temperature implementation based on a
single electronic spin in diamond, composite-pulse magnetometry provides a
tunable trade-off between sensitivities in the microT/sqrt(Hz) range,
comparable to those obtained with Ramsey spectroscopy, and coherence times
approaching T1
Sensing remote nuclear spins
Sensing single nuclear spins is a central challenge in magnetic resonance
based imaging techniques. Although different methods and especially diamond
defect based sensing and imaging techniques in principle have shown sufficient
sensitivity, signals from single nuclear spins are usually too weak to be
distinguished from background noise. Here, we present the detection and
identification of remote single C-13 nuclear spins embedded in nuclear spin
baths surrounding a single electron spins of a nitrogen-vacancy centre in
diamond. With dynamical decoupling control of the centre electron spin, the
weak magnetic field ~10 nT from a single nuclear spin located ~3 nm from the
centre with hyperfine coupling as weak as ~500 Hz is amplified and detected.
The quantum nature of the coupling is confirmed and precise position and the
vector components of the nuclear field are determined. Given the distance over
which nuclear magnetic fields can be detected the technique marks a firm step
towards imaging, detecting and controlling nuclear spin species external to the
diamond sensor
Controllable effects of quantum fluctuations on spin free-induction decay at room temperature
Fluctuations of local fields cause decoherence of quantum objects. Usually at high temperatures, thermal noises are much stronger than quantum fluctuations unless the thermal effects are suppressed by certain techniques such as spin echo. Here we report the discovery of strong quantum-fluctuation effects of nuclear spin baths on free-induction decay of single electron spins in solids at room temperature. We find that the competition between the quantum and thermal fluctuations is controllable by an external magnetic field. These findings are based on Ramsey interference measurement of single nitrogen-vacancy center spins in diamond and numerical simulation of the decoherence, which are in excellent agreement
Quantum control of proximal spins using nanoscale magnetic resonance imaging
Quantum control of individual spins in condensed matter systems is an
emerging field with wide-ranging applications in spintronics, quantum
computation, and sensitive magnetometry. Recent experiments have demonstrated
the ability to address and manipulate single electron spins through either
optical or electrical techniques. However, it is a challenge to extend
individual spin control to nanoscale multi-electron systems, as individual
spins are often irresolvable with existing methods. Here we demonstrate that
coherent individual spin control can be achieved with few-nm resolution for
proximal electron spins by performing single-spin magnetic resonance imaging
(MRI), which is realized via a scanning magnetic field gradient that is both
strong enough to achieve nanometric spatial resolution and sufficiently stable
for coherent spin manipulations. We apply this scanning field-gradient MRI
technique to electronic spins in nitrogen-vacancy (NV) centers in diamond and
achieve nanometric resolution in imaging, characterization, and manipulation of
individual spins. For NV centers, our results in individual spin control
demonstrate an improvement of nearly two orders of magnitude in spatial
resolution compared to conventional optical diffraction-limited techniques.
This scanning-field-gradient microscope enables a wide range of applications
including materials characterization, spin entanglement, and nanoscale
magnetometry.Comment: 7 pages, 4 figure
Nuclear spin pair coherence in diamond for atomic scale magnetometry
The nitrogen-vacancy (NV) centre, as a promising candidate solid state system
of quantum information processing, its electron spin coherence is influenced by
the magnetic field fluctuations due to the local environment. In pure diamonds,
the environment consists of hundreds of C-13 nuclear spins randomly spreading
in several nanometers range forming a spin bath. Controlling and prolonging the
electron spin coherence under the influence of spin bath are challenging tasks
for the quantum information processing. On the other hand, for a given bath
distribution, many of its characters are encoded in the electron spin
coherence. So it is natural to ask the question: is it possible to 'decode' the
electron spin coherence, and extract the information about the bath structures?
Here we show that, among hundreds of C-13 bath spins, there exist strong
coupling clusters, which give rise to the millisecond oscillations of the
electron spin coherence. By analyzing these oscillation features, the key
properties of the coherent nuclear spin clusters, such as positions,
orientations, and coupling strengths, could be uniquely identified. This
addressability of the few-nuclear-spin cluster extends the feasibility of using
the nuclear spins in diamond as qubits in quantum computing. Furthermore, it
provides a novel prototype of single-electron spin based, high-resolution and
ultra-sensitive detector for the chemical and biological applications.Comment: 15 pages, 4 figures, Nature Nanotechnology (2011
High-fidelity spin and optical control of single silicon-vacancy centres in silicon carbide
Scalable quantum networking requires quantum systems with quantum processing capabilities. Solid state spin systems with reliable spin–optical interfaces are a leading hardware in this regard. However, available systems suffer from large electron–phonon interaction or fast spin dephasing. Here, we demonstrate that the negatively charged silicon-vacancy centre in silicon carbide is immune to both drawbacks. Thanks to its 4A2 symmetry in ground and excited states, optical resonances are stable with near-Fourier-transform-limited linewidths, allowing exploitation of the spin selectivity of the optical transitions. In combination with millisecond-long spin coherence times originating from the high-purity crystal, we demonstrate high-fidelity optical initialization and coherent spin control, which we exploit to show coherent coupling to single nuclear spins with ∼1 kHz resolution. The summary of our findings makes this defect a prime candidate for realising memory-assisted quantum network applications using semiconductor-based spin-to-photon interfaces and coherently coupled nuclear spins
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
A robust, scanning quantum system for nanoscale sensing and imaging
Controllable atomic-scale quantum systems hold great potential as sensitive
tools for nanoscale imaging and metrology. Possible applications range from
nanoscale electric and magnetic field sensing to single photon microscopy,
quantum information processing, and bioimaging. At the heart of such schemes is
the ability to scan and accurately position a robust sensor within a few
nanometers of a sample of interest, while preserving the sensor's quantum
coherence and readout fidelity. These combined requirements remain a challenge
for all existing approaches that rely on direct grafting of individual solid
state quantum systems or single molecules onto scanning-probe tips. Here, we
demonstrate the fabrication and room temperature operation of a robust and
isolated atomic-scale quantum sensor for scanning probe microscopy.
Specifically, we employ a high-purity, single-crystalline diamond nanopillar
probe containing a single Nitrogen-Vacancy (NV) color center. We illustrate the
versatility and performance of our scanning NV sensor by conducting
quantitative nanoscale magnetic field imaging and near-field single-photon
fluorescence quenching microscopy. In both cases, we obtain imaging resolution
in the range of 20 nm and sensitivity unprecedented in scanning quantum probe
microscopy
Fourier Magnetic Imaging with Nanoscale Resolution and Compressed Sensing Speed-up using Electronic Spins in Diamond
Optically-detected magnetic resonance using Nitrogen Vacancy (NV) color
centres in diamond is a leading modality for nanoscale magnetic field imaging,
as it provides single electron spin sensitivity, three-dimensional resolution
better than 1 nm, and applicability to a wide range of physical and biological
samples under ambient conditions. To date, however, NV-diamond magnetic imaging
has been performed using real space techniques, which are either limited by
optical diffraction to 250 nm resolution or require slow, point-by-point
scanning for nanoscale resolution, e.g., using an atomic force microscope,
magnetic tip, or super-resolution optical imaging. Here we introduce an
alternative technique of Fourier magnetic imaging using NV-diamond. In analogy
with conventional magnetic resonance imaging (MRI), we employ pulsed magnetic
field gradients to phase-encode spatial information on NV electronic spins in
wavenumber or k-space followed by a fast Fourier transform to yield real-space
images with nanoscale resolution, wide field-of-view (FOV), and compressed
sensing speed-up.Comment: 31 pages, 10 figure
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