Search

Abstract: The organic inclusion compound 2,4,6-tris-(4-bromophenoxy)-1,3,5-triazine was used to create an ordered arrangement of the endohedral fullerenes N@C60 and P@C60 in a crystalline host matrix. Two different host–guest structures were investigated by X-ray diffraction and electron paramagnetic resonance. In one of these, an axial deformation of the fullerene guests leads to a sizeable zero-field splitting of the quartet ground state of the encapsulated atoms. The small size of the zero-field strain leads to well-separated lines for all transitions, opening the possibility of transition selective pulses for future quantum computing experiments in these multi-level systems. [Copyright &y& Elsevier]

Diamond provides unique technological platform for quantum technologies including quantum computing and communication. Controlled fabrication of optically active defects is a key element for such quantum toolkit. Here we report the production of single color centers emitting in the blue spectral region by high energy implantation of carbon ions. We demonstrate that single implanted defects show sub-poissonian statistics of the emitted photons and can be explored as single photon source in quantum cryptography. Strong zero phonon line at 470.5 nm allows unambiguous identification of this defect as interstitial-related TR12 color center. [ABSTRACT FROM AUTHOR]

Compact high-effectiveness counter-flow heat exchangers (CFHEX) are an essential building block of remote cooling systems and Reverse Turbo-Brayton coolers. This technology enables a wide variety of on-ground and space applications, including the cooling of infrared detectors, cryogenic chains of quantum computers and ultra-sensitive superconducting SQUID sensors. A mesh-based CFHEX design was previously proposed for such applications and demonstrated a great potential to meet the high effectiveness and compactness needs [1]. This paper presents a novel improved mesh-based CFHEX concept with a "transparent" inner wall and outlines the methods used for its manufacturing. Two of such CFHEXs are constructed and integrated in a technology demonstrator of a remote cooling system. Their performance is tested in the ▪ temperature, 1 bar–5 bar pressure and 50 mg/s–250 mg/s helium mass flow rate ranges. An effectiveness of ▪ (NTU=39–124) has been experimentally achieved with a pressure drop of less than 10 mbar per stream at the nominal operating conditions of the system. The experimental effectiveness and pressure drop results are analysed and compared to numerical predictions. The implications of the achieved high effectiveness on the final performance of the designed remote cooling system are also discussed. • Novel transparent-wall heat exchanger (HEX) design based on woven metal mesh reaches a remarkably high effectiveness. • Developed additive manufacturing method allows to fabricate mechanically sound mesh-based high-effectiveness cryogenic HEXs. • Proposed friction factor models for different woven mesh enable accurate HEX pressure drop predictions in various conditions. • Remote cooling systems based on novel HEXs have a great potential to reduce disturbances transported to the cooled object. [ABSTRACT FROM AUTHOR]

It was recently demonstrated that bulk nuclear polarization can be obtained using nitrogen vacancy (NV) color centers in diamonds, even at ambient conditions. This is based on the optical polarization of the NV electron spin, and using several polarization transfer methods. One such method is the nuclear orientation via electron spin locking (NOVEL) sequence, where a spin-locked sequence is applied on the NV spin, with a microwave power equal to the nuclear precession frequency. This was performed at relatively high fields, to allow for both polarization transfer and noise decoupling. As a result, this scheme requires accurate magnetic field alignment in order preserve the NV properties. Such a requirement may be undesired or impractical in many practical scenarios. Here we present a new sequence, termed the refocused NOVEL, which can be used for polarization transfer (and detection) even at low fields. Numerical simulations are performed, taking into account both the spin Hamiltonian and spin decoherence, and we show that, under realistic parameters, it can outperform the NOVEL sequence. [ABSTRACT FROM AUTHOR]

The loss of coherence is one of the main obstacles for the implementation of quantum information processing. The efficiency of dynamical decoupling schemes, which have been introduced to address this problem, is limited itself by the fluctuations in the driving fields which will themselves introduce noise. We address this challenge by introducing the concept of concatenated continuous dynamical decoupling, which can overcome not only external magnetic noise but also noise due to fluctuations in driving fields. We show theoretically that this approach can achieve relaxation limited coherence times, and demonstrate experimentally that already the most basic implementation of this concept yields an order of magnitude improvement to the decoherence time for the electron spin of nitrogen vacancy centers in diamond. The proposed scheme can be applied to a wide variety of other physical systems, including trapped atoms and ions and quantum dots, and may be combined with other quantum technologies challenges such as quantum sensing and quantum information processing. [ABSTRACT FROM AUTHOR]

Single defects in diamond and especially negatively charged nitrogen vacancy (NV) centers are very promising quantum systems with wide applications in physics and biology. It was shown that their coherence properties can be strongly improved by growing ultrapure diamond with low concentration of parasitic spins associated with nitrogen electron spins and nuclear spins related to 13C carbon isotope. Here we report a high quality 12C-enriched polycrystalline chemical vapor deposition diamond material with properties comparable with single crystals. We find single NVs in the grains of this material, which show extremely long electron spin coherence time T2>2ms. [ABSTRACT FROM AUTHOR]

Entanglement is the central yet fleeting phenomenon of quantum physics. Once being considered a peculiar counter-intuitive property of quantum theory, it has developed into the most central element of quantum technology. Consequently, there have been a number of experimental demonstrations of entanglement between photons, atoms, ions and solid-state systems such as spins or quantum dots, superconducting circuits and macroscopic diamond. Here we experimentally demonstrate entanglement between two engineered single solid-state spin quantum bits (qubits) at ambient conditions. Photon emission of defect pairs reveals ground-state spin correlation. Entanglement (fidelity = 0.67±0.04) is proved by quantum state tomography. Moreover, the lifetime of electron spin entanglement is extended to milliseconds by entanglement swapping to nuclear spins. The experiments mark an important step towards a scalable room-temperature quantum device being of potential use in quantum information processing as well as metrology. [ABSTRACT FROM AUTHOR]

We investigate the charging state of an isolated single dangling bond formed on an unpassivated Si(100) surface with c(4 χ 2) reconstruction, by comparing scanning tunneling microscopy and spectroscopy analysis with density functional theory calculations. The dangling bond is created by placing a single hydrogen atom on the bare surface with the tip of a scanning tunneling microscope. The Η atom passivates one of the dimer dangling bonds responsible for the surface one-dimensional electronic structure. This leaves a second dangling at the reacted surface dimer which breaks the surface periodicity. We consider two possible Η adsorption configurations for both the neutral and the doped situation (n- and p-type). In the case of n-doping we find that the single dangling bond state is doubly occupied and the most stable configuration is that with Η bonded to the bottom Si atom of the surface dimer In the case of p-doping the dangling bond is instead empty and the configuration with the Η attached to the top atom of the dimer is the most stable. Importandy the two configurations have different scattering properties and phase shift fingerprints. This might open up interesting perspectives for fabricating a switching device by tuning the doping level or by locally charging the single dangling bond state. [ABSTRACT FROM AUTHOR]

Abstract: The ultrafast dissociation dynamics of condensed water and ammonia by resonant core electron excitations have been studied by measuring the kinetic energy distributions of H+-ions desorbed by [N1s]4a1 and [O1s]4a1 excitations as a function of detuning, Δhν, from the center of the resonance. While the most probable ion energy varies monotonically with Δhν for both systems, the centers of gravity of the kinetic energy distributions are minimal at resonance and shift to higher kinetic energy with detuning to either lower or higher hν. This behavior is explained by contributions from bond evolution processes before and after the core hole decay. [Copyright &y& Elsevier]

We investigate the effect of surface termination on the charge state of nitrogen-vacancy (NV) centers, which have been ion-implanted a few nanometers below the surface of diamond. We find that, when changing the surface termination from oxygen to hydrogen, previously stable NV- centers convert into NV0 and, subsequently, into an unknown nonfluorescent state. This effect is found to depend strongly on the implantation dose. Simulations of the electronic band structure confirm the disappearance of NV- in the vicinity of the hydrogen-terminated surface. The band bending, which induces a p-type surface conductive layer, leads to a depletion of electrons in the nitrogen-vacancies close to the surface. Therefore, hydrogen surface termination provides a chemical way to control the charge state of nitrogen-vacancy centers in diamond. Furthermore, it opens the way to electrostatic control of the charge state with the use of an external gate electrode. [ABSTRACT FROM AUTHOR]

Devices that harness the laws of quantum physics hold the promise for information processing that outperforms their classical counterparts, and for unconditionally secure communication. However, in particular, implementations based on condensed-matter systems face the challenge of short coherence times. Carbon materials, particularly diamond, however, are suitable for hosting robust solid-state quantum registers, owing to their spin-free lattice and weak spin–orbit coupling. Here we show that quantum logic elements can be realized by exploring long-range magnetic dipolar coupling between individually addressable single electron spins associated with separate colour centres in diamond. The strong distance dependence of this coupling was used to characterize the separation of single qubits (98±3 Å) with an accuracy close to the value of the crystal-lattice spacing. Our demonstration of coherent control over both electron spins, conditional dynamics, selective readout as well as switchable interaction should open the way towards a viable room-temperature solid-state quantum register. As both electron spins are optically addressable, this solid-state quantum device operating at ambient conditions provides a degree of control that is at present available only for a few systems at low temperature. [ABSTRACT FROM AUTHOR]

Efficient polarization of organic molecules is of extraordinary relevance when performing nuclear magnetic resonance (NMR) and imaging. Commercially available routes to dynamical nuclear polarization (DNP) work at extremely low temperatures, relying on the solidification of organic samples and thus bringing the molecules out of their ambient thermal conditions. In this work, we investigate polarization transfer from optically pumped nitrogen vacancy centers in diamond to external molecules at room temperature. This polarization transfer is described by both an extensive analytical analysis and numerical simulations based on spin bath bosonization and is supported by experimental data in excellent agreement. These results set the route to hyperpolarization of diffusive molecules in different scenarios and consequently, due to an increased signal, to high-resolution NMR. [ABSTRACT FROM AUTHOR]

We report on the noise spectrum experienced by few nanometer deep nitrogen-vacancy centers in diamond as a function of depth, surface coating, magnetic field and temperature. Analysis reveals a double- Lorentzian noise spectrum consistent with a surface electronic spin bath in the low frequency regime, along with a faster noise source attributed to surface-modified phononic coupling. These results shed new light on the mechanisms responsible for surface noise affecting shallow spins at semiconductor interfaces, and suggests possible directions for further studies. We demonstrate dynamical decoupling from the surface noise, paving the way to applications ranging from nanoscale NMR to quantum networks. [ABSTRACT FROM AUTHOR]

Nitrogen impurities help to stabilize the negatively-charged-state of NV- in diamond, whereas magnetic fluctuations from nitrogen spins lead to decoherence of NV- qubits. It is not known what donor concentration optimizes these conflicting requirements. Here we used 10-MeV 15N3+ ion implantation to create NV- in ultrapure diamond. Optically detected magnetic resonance of single centers revealed a high creation yield of 40 ± 3% from 15N3+ ions and an additional yield of 56 ± 3% from 14N impurities. High-temperature anneal was used to reduce residual defects, and charge stable NV-, even in a dilute 14N impurity concentration of 0.06 ppb were created with long coherence times. [ABSTRACT FROM AUTHOR]

Spins of negatively charged nitrogen-vacancy (NV−) defects in diamond are among the most promising candidates for solid-state qubits. The fabrication of quantum devices containing these spin-carrying defects requires position-controlled introduction of NV− defects having excellent properties such as spectral stability, a long spin coherence time, and a stable negative charge state. Nitrogen ion implantation and annealing enable the positioning of NV− spin qubits with high precision, but to date, the coherence times of qubits produced this way are short, presumably because of the presence of residual radiation damage. In the present work, we demonstrate that a high-temperature annealing at 1000 ∘C allows 2 ms coherence times to be achieved at room temperature. These results were obtained for implantation-produced NV− defects in a high-purity, 99.99% 12C-enriched single crystal chemical vapor deposited diamond. We discuss these long coherence times in the context of the thermal behavior of residual defect spins. [ABSTRACT FROM AUTHOR]

We report the detection and polarization of nuclear spins in diamond at room temperature by using a single nitrogen-vacancy (NV) center. We use Hartmann-Hahn double resonance to coherently enhance the signal from a single nuclear spin while decoupling from the noisy spin bath, which otherwise limits the detection sensitivity. As a proof of principle, we (i) observe coherent oscillations between the NV center and a weakly coupled nuclear spin and (ii) demonstrate nuclear-bath cooling, which prolongs the coherence time of the NV sensor by more than a factor of 5. Our results provide a route to nanometer scale magnetic resonance imaging and novel quantum information processing protocols. [ABSTRACT FROM AUTHOR]

Nanometer-sizeddiamonds containing nitrogen-vacancy defect centers(NV) are promising nanosensors in biological environments due to theirbiocompatibility, bright fluorescence, and high magnetic sensitivityat ambient conditions. Here we report on the detection of ferritinmolecules using magnetic noise induced by the inner paramagnetic ironas a contrast mechanism. We observe a significant reduction of bothcoherence and relaxation time due to the presence of ferritin on thesurface of nanodiamonds. Our theoretical model is in excellent agreementwith the experimental data and establishes this method as a novelsensing technology for proteins. [ABSTRACT FROM AUTHOR]

We present a solid state magnetic field imaging technique using a two-dimensional array of spins in diamond. The magnetic sensing spin array is made of nitrogen vacancy (NV) centers created at shallow depths. Their optical response is used for measuring external magnetic fields in close proximity. Optically detected magnetic resonance is read out from a 60×60 μm2 field of view in a multiplexed manner using a charge coupled device camera. We experimentally demonstrate full two-dimensional vector imaging of the magnetic field produced by a pair of current carrying microwires. The presented wide-field NV magnetometer offers, in addition to its high magnetic sensitivity and vector reconstruction, an unprecedented spatiotemporal resolution and functionality at room temperature. [ABSTRACT FROM AUTHOR]

We describe a technique for fabricating micro- and nanostructures incorporating fluorescent defects in diamond with a positional accuracy better than hundreds of nanometers. Using confocal fluorescence microscopy and focused ion beam etching, we initially locate a suitable defect with respect to registration marks on the diamond surface then etch a structure using these coordinates. We demonstrate the technique by etching an 8 μm diameter hemisphere positioned with single negatively charged nitrogen-vacancy defect lies at its origin. Direct comparison of the fluorescence photon count rate before and after fabrication shows an eightfold increase due to the presence of the hemisphere. [ABSTRACT FROM AUTHOR]

We present a flexible scheme to realize non-Markovian dynamics of an electronic spin qubit, using a nitrogen-vacancy center in diamond where the inherent nitrogen spin serves as a regulator of the dynamics. By changing the population of the nitrogen spin, we show that we can smoothly tune the non-Markovianity of the electron spin's dynamics. Furthermore, we examine the decoherence dynamics induced by the spin bath to exclude other sources of non-Markovianity. The amount of collected measurement data is kept at a minimum by employing Bayesian data analysis. This allows for a precise quantification of the parameters involved in the description of the dynamics and a prediction of so far unobserved data points. [ABSTRACT FROM AUTHOR]