1,193 research outputs found
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
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
Quantum control of hybrid nuclear-electronic qubits
Pulsed magnetic resonance is a wide-reaching technology allowing the quantum
state of electronic and nuclear spins to be controlled on the timescale of
nanoseconds and microseconds respectively. The time required to flip either
dilute electronic or nuclear spins is orders of magnitude shorter than their
decoherence times, leading to several schemes for quantum information
processing with spin qubits. We investigate instead the novel regime where the
eigenstates approximate 50:50 superpositions of the electronic and nuclear spin
states forming "hybrid nuclear-electronic" qubits. Here we demonstrate quantum
control of these states for the first time, using bismuth-doped silicon, in
just 32 ns: this is orders of magnitude faster than previous experiments where
pure nuclear states were used. The coherence times of our states are five
orders of magnitude longer, reaching 4 ms, and are limited by the
naturally-occurring 29Si nuclear spin impurities. There is quantitative
agreement between our experiments and no-free-parameter analytical theory for
the resonance positions, as well as their relative intensities and relative
Rabi oscillation frequencies. In experiments where the slow manipulation of
some of the qubits is the rate limiting step, quantum computations would
benefit from faster operation in the hybrid regime.Comment: 20 pages, 8 figures, new data and simulation
Towards a large-scale quantum simulator on diamond surface at room temperature
Strongly-correlated quantum many-body systems exhibits a variety of exotic
phases with long-range quantum correlations, such as spin liquids and
supersolids. Despite the rapid increase in computational power of modern
computers, the numerical simulation of these complex systems becomes
intractable even for a few dozens of particles. Feynman's idea of quantum
simulators offers an innovative way to bypass this computational barrier.
However, the proposed realizations of such devices either require very low
temperatures (ultracold gases in optical lattices, trapped ions,
superconducting devices) and considerable technological effort, or are
extremely hard to scale in practice (NMR, linear optics). In this work, we
propose a new architecture for a scalable quantum simulator that can operate at
room temperature. It consists of strongly-interacting nuclear spins attached to
the diamond surface by its direct chemical treatment, or by means of a
functionalized graphene sheet. The initialization, control and read-out of this
quantum simulator can be accomplished with nitrogen-vacancy centers implanted
in diamond. The system can be engineered to simulate a wide variety of
interesting strongly-correlated models with long-range dipole-dipole
interactions. Due to the superior coherence time of nuclear spins and
nitrogen-vacancy centers in diamond, our proposal offers new opportunities
towards large-scale quantum simulation at room temperatures
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
Topologically Protected Quantum State Transfer in a Chiral Spin Liquid
Topology plays a central role in ensuring the robustness of a wide variety of
physical phenomena. Notable examples range from the robust current carrying
edge states associated with the quantum Hall and the quantum spin Hall effects
to proposals involving topologically protected quantum memory and quantum logic
operations. Here, we propose and analyze a topologically protected channel for
the transfer of quantum states between remote quantum nodes. In our approach,
state transfer is mediated by the edge mode of a chiral spin liquid. We
demonstrate that the proposed method is intrinsically robust to realistic
imperfections associated with disorder and decoherence. Possible experimental
implementations and applications to the detection and characterization of spin
liquid phases are discussed.Comment: 14 pages, 7 figure
Regulation of cell survival by sphingosine-1-phosphate receptor S1P1 via reciprocal ERK-dependent suppression of bim and PI-3-kinase/protein kinase C-mediated upregulation of Mcl-1
Although the ability of bioactive lipid sphingosine-1-phosphate (S1P) to positively regulate anti-apoptotic/pro-survival responses by binding to S1P1 is well known, the molecular mechanisms remain unclear. Here we demonstrate that expression of S1P1 renders CCL39 lung fibroblasts resistant to apoptosis following growth factor withdrawal. Resistance to apoptosis was associated with attenuated accumulation of pro-apoptotic BH3-only protein Bim. However, although blockade of extracellular signal-regulated kinase (ERK) activation could reverse S1P1-mediated suppression of Bim accumulation, inhibition of caspase-3 cleavage was unaffected. Instead S1P1-mediated inhibition of caspase-3 cleavage was reversed by inhibition of phosphatidylinositol-3-kinase (PI3K) and protein kinase C (PKC), which had no effect on S1P1 regulation of Bim. However, S1P1 suppression of caspase-3 was associated with increased expression of anti-apoptotic protein Mcl-1, the expression of which was also reduced by inhibition of PI3K and PKC. A role for the induction of Mcl-1 in regulating endogenous S1P receptor-dependent pro-survival responses in human umbilical vein endothelial cells was confirmed using S1P receptor agonist FTY720-phosphate (FTY720P). FTY720P induced a transient accumulation of Mcl-1 that was associated with a delayed onset of caspase-3 cleavage following growth factor withdrawal, whereas Mcl-1 knockdown was sufficient to enhance caspase-3 cleavage even in the presence of FTY720P. Consistent with a pro-survival role of S1P1 in disease, analysis of tissue microarrays from ER+ breast cancer patients revealed a significant correlation between S1P1 expression and tumour cell survival. In these tumours, S1P1 expression and cancer cell survival were correlated with increased activation of ERK, but not the PI3K/PKB pathway. In summary, pro-survival/anti-apoptotic signalling from S1P1 is intimately linked to its ability to promote the accumulation of pro-survival protein Mcl-1 and downregulation of pro-apoptotic BH3-only protein Bim via distinct signalling pathways. However, the functional importance of each pathway is dependent on the specific cellular context
Probing host pathogen cross-talk by transcriptional profiling of both Mycobacterium tuberculosis and infected human dendritic cells and macrophages
This study provides the proof of principle that probing the host and the microbe transcriptomes simultaneously is a valuable means to accessing unique information on host pathogen interactions. Our results also underline the extraordinary plasticity of host cell and pathogen responses to infection, and provide a solid framework to further understand the complex mechanisms involved in immunity to M. tuberculosis and in mycobacterial adaptation to different intracellular environments
The related-key analysis of feistel constructions
Lecture Notes in Computer Science, Volume 8540, 2015.It is well known that the classical three- and four-round Feistel constructions are provably secure under chosen-plaintext and chosen-ciphertext attacks, respectively. However, irrespective of the
number of rounds, no Feistel construction can resist related-key attacks where the keys can be offset by a constant. In this paper we show that, under suitable reuse of round keys, security under related-key attacks can be provably attained. Our modification is substantially simpler and more efficient than alternatives obtained using generic transforms, namely the PRG transform of Bellare and Cash (CRYPTO 2010) and its random-oracle analogue outlined by Lucks (FSE 2004). Additionally we formalize Luck’s transform and show that it does not always work if related keys are derived in an oracle-dependent way, and then prove it sound under appropriate restrictions
Nanoscale magnetic imaging of a single electron spin under ambient conditions
The detection of ensembles of spins under ambient conditions has revolutionized the biological, chemical and physical sciences through magnetic resonance imaging and nuclear magnetic resonance . Pushing sensing capabilities to the individual-spin level would enable unprecedented applications such as single-molecule structural imaging; however, the weak magnetic fields from single spins are undetectable by conventional far-field resonance techniques . In recent years, there has been a considerable effort to develop nanoscale scanning magnetometers , which are able to measure fewer spins by bringing the sensor in close proximity to its target. The most sensitive of these magnetometers generally require low temperatures for operation, but the ability to measure under ambient conditions (standard temperature and pressure) is critical for many imaging applications, particularly in biological systems. Here we demonstrate detection and nanoscale imaging of the magnetic field from an initialized single electron spin under ambient conditions using a scanning nitrogen-vacancy magnetometer. Real-space, quantitative magnetic-field images are obtained by deterministically scanning our nitrogen-vacancy magnetometer 50 nm above a target electron spin, while measuring the local magnetic field using dynamically decoupled magnetometry protocols. We discuss how this single-spin detection enables the study of a variety of room-temperature phenomena in condensed-matter physics with an unprecedented combination of spatial resolution and spin sensitivity
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