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The spin resonance clock transition of the endohedral fullerene $^{15}\mathrm{N@C}_{60}
Abstract
The endohedral fullerene has narrow electron paramagnetic resonance lines which have been proposed as the basis for a condensed-matter portable atomic clock. We measure the low-frequency spectrum of this molecule, identifying and characterizing a clock transition at which the frequency becomes insensitive to magnetic field. We infer a linewidth at the clock field of 100 kHz. Using experimental data, we are able to place a bound on the clock's projected frequency stability. We discuss ways to improve the frequency stability to be competitive with existing miniature clocks.
... The experimental demonstration of this clock transition requires a specially designed spectrometer which is currently under way in our lab to evaluate the potential of 2 H@POSS as a spin-based atomic clock device. Although there are EPR systems where clock transitions have been identified as important elements for quantum computing [10,[26][27][28][29][30], the simplicity of atomic hydrogen together with the stability of POSS cages and the access of resonances Content courtesy of Springer Nature, terms of use apply. Rights reserved. ...
... In the literature, other interesting cases have been reported such as 15 N@C 60 (S = 3∕2, I = 1∕2) [10], 51 V(III) impurities in MgO ( S = 3∕2, I = 7∕2 ) [35], 31 P in Si ( S = 1∕2, I = 1∕2 ) [36], and 209 Bi in Si ( S = 1∕2, I = 9∕2 ) [37][38][39]. As has been mentioned, the parallel-mode transitions are enhanced in the case of large hyperfine interactions and small magnetic fields (low microwave frequencies). ...
... Therefore, in these cases, the parallel-mode transitions can be hardly observed at X-band. In the case of 15 N@C 60 , the parallel-mode transitions were observed at very low microwave frequencies [10]. An interesting exception is the case of 209 Bi in Si. 209 Bi has a nuclear spin of 9/2 and a remarkably large hyperfine interaction (1475.4 ...
In a typical EPR experiment, the transitions require that the static magnetic field B0 is oriented perpendicular to the microwave field B1 (perpendicular mode). This is determined by the transition rules either in the classical or in the quantum mechanical description. However, there are cases where EPR transitions are observed when B0 is oriented parallel to B1 (parallel mode). Quite numerous studies can be found in the literature where EPR transitions in both modes (dual-mode EPR) are feasible. In the majority of cases, dual-mode EPR studies are typically applied in S>1/2 systems where non-zero transition probabilities for the parallel mode are the result of the state mixing provided by the zero-field splitting interaction. On the other hand, the observation of parallel-mode EPR signals in S=1/2 systems becomes feasible when strong hyperfine interaction between the electronic and nuclear spin is present, as has been theoretically predicted for the hydrogen atom having a hyperfine coupling constant of A0=1420 MHz (Weil in Concepts Magn Reson Part A 28:331, 2006). Herein, we report the first dual-mode X-band EPR experiments of hydrogen atom (both isotopes 1H and 2H) encapsulated in polyhedral oligomeric silsesquioxane cages. We extend the theory to the case of deuterium and we extract analytical formulas for transition probabilities. For the forbidden transitions, this study revealed a first-order dependence of resonance fields on the nuclear g-factor, gn, and the existence of a clock transition with f=307 MHz.
... Clock transition, a transition with a relatively stable frequency that is not affected by fluctuation of the external magnetic field, has been observed in endohedral fullerene ( Figure 1G). Such property makes it a promising candidate toward solid-state molecular clock applications because all directions of magnetic field fluctuation can be effectively mitigated [6]. Compared with ammonia clock using gas cells, the solid-state design is advantageous for miniaturization. ...
... (G) Solid-state atomic clock transitions for frequency standard. Reproduced with the permission of ref.[6]. (H) Addressable multi-level transitions to implement geomatic phase gate. ...
... Our interest is in molecular systems, for which enhanced coherence was demonstrated at a clock transition for a [Ho(W 5 O 18 ) 2 ] 9− molecule by Shiddiq et al. 17 . Subsequently, clock transitions have been studied in other molecular systems [18][19][20][21][22] and the effects of structural distortions have been analyzed theoretically for several Ho III and V IV complexes 23 . ...
The ability to design quantum systems that decouple from environmental noise sources is highly desirable for development of quantum technologies with optimal coherence. The chemical tunability of electronic states in magnetic molecules combined with advanced electron spin resonance techniques provides excellent opportunities to address this problem. Indeed, so-called clock transitions have been shown to protect molecular spin qubits from magnetic noise, giving rise to significantly enhanced coherence. Here we conduct a spectroscopic and computational investigation of this physics, focusing on the role of the nuclear bath. Away from the clock transition, linear coupling to the nuclear degrees of freedom causes a modulation and decay of electronic coherence, as quantified via electron spin echo signals generated experimentally and in silico. Meanwhile, the effective hyperfine interaction vanishes at the clock transition, resulting in electron-nuclear decoupling and an absence of quantum information leakage to the nuclear bath, providing opportunities to characterize other decoherence sources.
... We do note a relatively recent acknowledgment that some specific organic species may also be useful quantum mimics of atomic clocks, if they contain N-centered radicals. [164,165] The main design strategy in all of these cases is that the magnetic interaction has to compete with the energy of the spin's interaction with an applied magnetic field. In other words, the two interactions must stabilize different ground levels, as this will create crossing points with changing field that turn to avoided crossings. ...
Quantum objects, such as atoms, spins, and subatomic particles, haveunique physical properties that could be useful for many different applications, ranging from quantum information processing to magnetic resonance imaging. Molecular species also exhibit these quantum properties, and, importantly, these properties are fundamentally tunable by synthetic design, unlike ions isolated in a quadrupolar trap, for example. In this comment, we distill multiple, distinct, scientific efforts into an emergent field that is devoted to designing molecules that mimic the quantum properties of objects like trapped atoms or defects in solids. Mimicry is endemic in inorganic chemistry and featured heavily in the research interests of groups across the world. We describe this new field of using molecular inorganic chemistry to mimic the quantum properties (e.g. the lifetime of spin superpositions, or the resonant frequencies thereof) of other quantum objects as “quantum mimicry.” In this comment, we describe the philosophical design strategies and recent exciting results from the application of these strategies.
... Further endohedral systems can act as acceptor materials for increasing the efficiency of photovoltaic devices [26]. Many other applications of endohedral systems for designing hydrogen storage devices [27], gas sensors [28] and condensed matter atomic clocks [29] have been envisaged recently and these systems also find applications in biomedical fields as well [30]. Photoionization studies of endohedral systems provide many important information about such systems and understanding their ionization spectra is very important considering the potential applications both at the fundamental and practical perspectives. ...
The photoionization cross-section of an atom trapped inside a fullerene anion in the near-threshold region is dominated by the Coulomb confinement resonances. These prominent structures facilitate the possibility of an enhanced spin–orbit interaction activated interchannel coupling (SOIAIC) leading to significant modifications of the photoionization parameters even for low-Z confined atomic systems. The existence of such confinement enhanced SOIAIC structures are demonstrated for the relativistically split 2p ionization channels of Ar trapped inside fullerene anion. Dramatic modifications are observed not only in the cross-sections but also in the angular distributions, and relative phases between the degenerate channels present. Similar structures are found for the case of confined Kr as well. A detailed analysis of these interesting features is carried out which showed the importance of correlation and relativistic effects on the photoionization dynamics of confined atomic systems.
... While an increasing number of candidate molecules showing sufficiently long spin relaxation times have been synthesized, pushing the limit to the millisecond scale 13 , fullerenes are uniquely advantageous because these allcarbon molecules have little intramolecular hyperfine interaction, which helps preserving the spin coherence, and the near-spherical symmetry of the cage configurations allows small zero-field splittings (ZFS) [14][15][16][17] . As a result, various studies related to fullerene-based quantum information processing (QIP) have been reported, studying the ultrafast control of nuclear spin qubits assisted by electron spin 18,19 , the entanglement between electron and nuclear spins 20,21 , electron spin dipolar coupling 22,23 and the atomic clock transition 24 . ...
High-spin magnetic molecules are promising candidates for quantum information processing because their intrinsic multiplicity facilitates information storage and computational operations. However, due to the absence of suitable sublevel splittings, their susceptibility to environmental disturbances and limitation from the selection rule, the arbitrary control of the quantum state of a molecular electron multiplet has not been realized. Here, we exploit the photoexcited triplet of C 70 as a molecular electron spin qutrit with pulsed electron paramagnetic resonance. We prepared the system into 3-level superposition states characteristic of a qutrit and validated them by the tomography of their density matrices. To further elucidate the coherence of the operation and the nature of the system as a qutrit, we demonstrated the quantum phase interference in the superposition. The interference pattern is further interpreted as a map of possible evolution paths in the space of phase factors, representing the quantum nature of the 3-level system.
... 1-3 While an increasing number of new candidate molecules showing sufficiently long spin relaxation times have been synthesized recently, 4 fullerenes are still advantageous because their spin coherence is inherently preserved, which is associated with the clean intramolecular magnetic environment of carbon nuclei and the near-spherical symmetry of the cage configuration. [5][6][7][8] As a result, regarding fullerene-based QIP, ultrafast control of nuclear spin qubits assisted by electron spin, 9,10 entanglement between electron and nuclear spins, 11,12 electron spin dipolar coupling 13,14 and fullerene-based atomic clock transition, 15 has been studied experimentally. One of the most promising advantages of magnetic molecules is their ease of being scaled up and made into spin systems of higher nuclearity or dimension, which can be used to encode more information. ...
High spin magnetic molecules are promising candidates for quantum information processing because they intrinsically have multiple sublevels for information storage and computational operations. However, due to their susceptibility to the environment and limitation from the selection rule, the arbitrary control of the quantum state of a multilevel system on a molecular and electron spin basis has not been realized. Here we exploit the photoexcited triplet of C70 as a molecular electron spin qutrit. After the system was initialized by photoexcitation, we prepared it into representative three-level superposition states characteristic of the qutrit, measured their density matrices, and showed the interference of the quantum phases in the superposition. The interference pattern is further interpreted as a map of evolution through time under different conditions.
... 6 In particular, 15 N@C 60 is suitable as a frequency reference due to its sharp resonances 7 and the existence of a clock transition in its low-field spectrum. 8 Since the frequency of this clock transition depends solely on the isotropic hyperfine coupling constant A, it is important to characterise the mechanisms that affect it. For example, the hyperfine coupling is known to depend on temperature, 9 which could reduce the long term stability of a fullerene clock against environmental temperature fluctuations. ...
We measure the electron spin resonance spectrum of the endohedral fullerene molecule at pressures ranging from atmospheric pressure to 0.25 GPa, and find that the hyperfine coupling increases linearly with pressure. We present a model based on van der Waals interactions, which accounts for this increase via compression of the fullerene cage and consequent admixture of orbitals with a larger hyperfine coupling. Combining this model with theoretical estimates of the bulk modulus, we predict the pressure shift and compare it to our experimental results, finding fair agreement given the spread in estimates of the bulk modulus. The spin resonance linewidth is also found to depend on pressure. This is explained by considering the pressure-dependent viscosity of the solvent, which modifies the effect of dipolar coupling between spins within fullerene clusters.
Fullerenes have a unique structure, capable of both encapsulating other molecules and reacting with those on the exterior surface. Fullerene derivatives have also been found to have enormous potential to address the challenges of the renewable energy sector and current environmental issues, such as in the production of n-type materials in bulk heterojunction solar cells, as antimicrobial agents, in photocatalytic water treatment processes, and in sensor technologies. Endohedral metallofullerenes, in particular, can possess unpaired electron spins, driven by the enclosed metal atom or cluster, which yield valuable magnetic properties. These properties have significant potential for applications in molecular magnets, spin probes, quantum computing, and devices such as quantum information processing,, atomic clocks, and molecular magnets. However, the intrinsically low yield of endohedral fullerenes remains a huge obstacle, impeding not only their industrial utilization but also the synthesis and characterization essential for exploring novel applications. The low yield and difficulty in separation of different types of endohedral fullerenes results in the usage of a large amount of solvents and energy, which is detrimental to the environment. In this paper, we analyse the methodologies proposed by various researchers and identify the critical synthesis parameters that play a role in increasing the yields of fullerenes.
Coulomb confinement resonances (CCRs) are the main features of the photoionization spectra of an atom inside an anionic fullerene. These CCRs can act as an amplifier to spin-orbit-interaction-activated interchannel coupling (SOIAIC) and can lead to discernible signatures of relativistic effects even for low Z confined atomic systems. The present paper demonstrates this intriguing feature by studying angular photoemission time delay of the 2p3/2 subshell of Ar@C60−1 in the vicinity of the 2p1/2 ionization threshold. Here 2p1/2 CCR functions as an amplifier to the SOIAIC and, thereby, induces significant modifications in the 2p3/2 angular time delay through the interchannel coupling. Moreover, the effects of the SOIAIC for the spin-up and spin-down photoelectrons are found to be different. All of these suggest that angle-resolved time-delay measurements can reveal the relativistic effects even for the low Z confined atomic systems, and Ar@C60−1 is a potential candidate for such experimental scrutiny. The impact of the model parameters on the predicted feature is also critically examined by using different sets of parameters. All of those calculations showed the existence of SOIAIC enabled structures in the angular time-delay profile.
Magnetic molecules have shown great potential in quantum information processing due to the chemical tunablity of their quantum behaviors. Chemical derivatives of endohedral nitrogen fullerenes with long coherence time and rich energy levels were synthesized and studied to demonstrate the ability of multiprocessing in quantum information using electron magnetic resonance. After initialization of the 12‐levelled spin system, subgroups of spin energy levels coursed by the hyperfine couplings can be selectively manipulated. The cooperatively combining of the parallel calculations enabled quantum error correction, increasing the correct rate by up to 17.82 %. Also, different subgroups of transitions divided by hyperfine coupling can be treated as independent qubits, and multi‐task quantum computing were realized by performing Z‐gate and X‐gate simultaneously, which accelerates the overall gating speed.
Magnetic molecules have shown great potential in quantum information processing due to the chemical tunablity of their quantum behaviors. Chemical derivatives of endohedral nitrogen fullerenes with long coherence time and rich energy levels were synthesized and studied to demonstrate the ability of multiprocessing in quantum information using electron magnetic resonance. After initialization of the 12‐levelled spin system, subgroups of spin energy levels coursed by the hyperfine couplings can be selectively manipulated. The cooperatively combining of the parallel calculations enabled quantum error correction, increasing the correct rate by up to 17.82%. Also, different subgroups of transitions divided by hyperfine coupling can be treated as independent qubits, and multi‐task quantum computing were realized by performing Z‐gate and X‐gate simultaneously, which accelerates the overall gating speed.
Realization of stable spin states in surface-supported magnetic molecules is crucial for their applications in molecular spintronic, memory storage or quantum information processing. In this work, we studied the surface...
Endohedral nitrogen fullerenes have been proposed as building blocks for quantum information processing due to their long spin coherence time. However, addressability of the individual electron spin levels in such a multiplet system of ⁴S3/2 has never been achieved because of the molecular isotropy and transition degeneracy among the Zeeman levels. Herein, by molecular engineering, we lifted the degeneracy by zero‐field splitting effects and made the multiple transitions addressable by a liquid‐crystal‐assisted method. The endohedral nitrogen fullerene derivatives with rigid addends of spiro structure and large aspect ratios of regioselective bis‐addition improve the ordering of the spin ensemble. These samples empower endohedral‐fullerene‐based qudits, in which the transitions between the 4 electron spin levels were respectively addressed and coherently manipulated. The quantum geometric phase manipulation, which has long been proposed for the advantages in error tolerance and gating speed, was implemented in a pure electron spin system using molecules for the first time.
Endohedral nitrogen fullerenes have been proposed as building blocks for quantum information processing due to their long spin coherence time. However, addressability of the individual electron spin levels in such a multiplet system of 4S3/2 has never been achieved because of the molecular isotropy and transition degeneracy among the Zeeman levels. Herein, by molecular engineering, we lifted the degeneracy by zero-field splitting effects and made the multiple transitions addressable by a liquid-crystal-assisted method. The endohedral nitrogen fullerene derivatives with rigid addends of spiro structure and large aspect ratios of regioselective bis-addition improve the ordering of the spin ensemble. These samples empower endohedral-fullerene-based qudits, in which the transitions between the 4 electron spin levels were respectively addressed and coherently manipulated. The quantum geometric phase manipulation, which has long been proposed for the advantages in error tolerance and gating speed, was implemented in a pure electron spin system using molecules for the first time.
The search for novel two-dimensional (2D) materials is crucial for the development of next generation technologies such as electronics, optoelectronics, electrochemistry and biomedicine. In this work, we designed a series of 2D materials based on endohedral fullerenes and revealed that many of them integrate different functions in a single system, such as ferroelectricity with large electric dipole moments, multiple magnetic phases with both strong magnetic anisotropy and high Curie temperature, and quantum spin Hall effect or quantum anomalous Hall effect with robust topologically protected edge states. We further proposed a new type of topological field-effect transistor. These findings provide a strategy for using fullerenes as building blocks for the synthesis of novel 2D materials which can be easily controlled with a local electric field.
Both exohedral and endohedral complexes of second row elements doped X12Y12 (X = B, Al and Y = P) nano-cages are evaluated for thermodynamic stabilities, electronic properties and kinetic barriers. Interaction energies are calculated to deeply perceive the stability of these complexes. Further, interconversion of exohedral and endohedral complexes is explored through an unprecedented approach, where 2nd row elements translate into nano-cages through boundary crossing. Subsequently, the kinetic barriers for encapsulation and decapsulation are also investigated through PES scanning of all elements by passing through hexagon of nano-cages. Systematic investigations revealed that due to larger diameter, AlP nanocage exhibits low encapsulation barriers in comparison to BP nano-cage. Such as; the encapsulation barrier of F@AlP (7.57 kcal mol-1) is lower than that of F@BP (129.78 kcal mol-1). Moreover, distortion of nano-cages due to translation of elements is also estimated by distortion energies. Large distortion energies of 113.81/118.39 kcal mol-1 are noticed for exo-B@AlP/exo-C@BP complexes. In addition, the electronic properties for all the complexes are probed and depicted that the endohedral doping have remarkable influence on the electronic properties of the nanocage in comparison to exohedral doping. NBO charge analysis shows that Be metal delivers charges of 0.08 |e|/0.03 |e| to the AlP/BP nanocage, causing the later more electron rich. Contrary to Be, all other doped atoms show negative charges.
Molecular spin qubits are chemical nanoobjects with promising applications that are so far hampered by the rapid loss of quantum information, a process known as decoherence. A strategy to improve...
Single crystal lithium ferrite (LiFe) spheres of sub-mm dimension are examined at mK temperatures, microwave frequencies, and variable dc magnetic field, for use in hybrid quantum systems and condensed matter and fundamental physics experiments. Strong coupling regimes of the photon-magnon interaction (cavity magnon polariton quasiparticles) were observed with coupling strength of up to 250 MHz at 9.5 GHz (2.6%) with magnon linewidths of order 4 MHz (with potential improvement to sub-MHz values). We show that the photon-magnon coupling can be significantly improved and exceed that of the widely used yttrium iron garnet crystal, due to the small unit cell of LiFe, allowing twice the spins per unit volume. Magnon mode softening was observed at low dc fields and, combined with the normal Zeeman effect, creates magnon spin-wave modes that are insensitive to first-order magnetic-field fluctuations. This effect is observed in the Kittel mode at 5.5 GHz (and another higher order mode at 6.5 GHz) with a dc magnetic field close to 0.19 tesla. We show that if the cavity is tuned close to this frequency, the magnon polariton particles exhibit an enhanced range of strong coupling and insensitivity to magnetic field fluctuations with both first-order and second-order insensitivity to magnetic field as a function of frequency (double magic point clock transition), which could potentially be exploited in cavity QED experiments.
In this article, we present an integrated broadband complementary metal-oxide semiconductor single-chip transceiver suitable for the realization of multi-nuclear pulsed nuclear magnetic resonance (NMR) probes. The realized single-chip transceiver can be interfaced with on-chip integrated microcoils or external LC resonators operating in the range from 1 MHz to 1 GHz. The dimension of the chip is about 1 mm2. It consists of a radio-frequency
(RF) power amplifier, a low-noise RF preamplifier, a frequency mixer, an audio-frequency amplifier, and fully integrated transmit-receive switches. As specific example, we show its use for multi-nuclear NMR spectroscopy. With an integrated coil of about 150 μm external diameter, a 1H spin sensitivity of about 1.5 × 1013 spins/Hz1/2 is achieved at 7 T.
This paper reviews currently recognized needs for advances in precision navigation and timing technology, summarizes ongoing efforts, and discusses future technological developments being pursued under the aggregated DARPA/MTO Microtechnology for Positioning, Navigation, and Timing (micro-PNT) program.
A major challenge in using spins in the solid state for quantum technologies is protecting them from sources of decoherence. This is particularly important in nanodevices where the proximity of material interfaces, and their associated defects, can play a limiting role. Spin decoherence can be addressed to varying degrees by improving material purity or isotopic composition, for example, or active error correction methods such as dynamic decoupling (or even combinations of the two). However, a powerful method applied to trapped ions in the context of atomic clocks is the use of particular spin transitions that are inherently robust to external perturbations. Here, we show that such 'clock transitions' can be observed for electron spins in the solid state, in particular using bismuth donors in silicon. This leads to dramatic enhancements in the electron spin coherence time, exceeding seconds. We find that electron spin qubits based on clock transitions become less sensitive to the local magnetic environment, including the presence of (29)Si nuclear spins as found in natural silicon. We expect the use of such clock transitions will be of additional significance for donor spins in nanodevices, mitigating the effects of magnetic or electric field noise arising from nearby interfaces and gates.
Well resolved EPR spectra of P@C60 in solution have been recorded, proving that the encased phosphorus atoms are in their quartet spin ground state. The isotropic hyperfine interaction is increased by a factor of 2.5 compared with the values measured for free atoms. An analysis of spin relaxation data reveals that fluctuating zero field splitting (ZFS) interaction induced by collision-induced deformations of the carbon shell constitutes the dominant relaxation mechanism. The variance of the time fluctuating ZFS interaction is about a factor of 10 larger than that observed for N@C60 under identical conditions. Values for the correlation time of the deformation of the fullerene cage range from 5ps to 32 ps in the temperature interval 190-300 K in toluene.
The size and operating power of the core physics assembly of an atomic clock was reduced using fabrication techniques. The device has the potential to bring atomically precise timing to hand-held, battery-operated devices, with a volume of 9.5 mm 3, a fractional frequency instability of 2.5×10 -10 at 1 s of integration and dissipating less than 75 mW of power. It was shown that the design and fabrication allows for wafer-level assembly of the structures and easy integration with other electronics. It was found that the atomic clock physics package displays an improvement over the previous state-of-the-art by a factor of 100 in volume and a factor of 10 in power dissipation.
In our earlier work, we developed a 2-kg NMR system, which was 60 X lighter, 40× smaller, yet 60× more spin-mass sensitive than a 120-kg state-of-the-art commercial benchtop system. Here we report on two new nuclear magnetic resonance (NMR) systems that represent further orders-of-magnitude size reduction and lab-on-a-chip capability. The first system, which weighs 0.1 kg and can be held in the palm of a hand, is the smallest NMR system ever built, and is 1200× lighter, 1200× smaller, yet 150× more spin-mass sensitive than the commercial system. It is enabled by combining the physics of NMR with a CMOS RF transceiver. The second system, which even integrates a sample coil, directly interfaces the CMOS chip with a sample for lab-on-a-chip operation. The two systems detect biological objects such as avidin, human chorionic gonadotropin, and human bladder cancer cells.
Endohedral N@C60 (atomic nitrogen inside C60) is produced by ion implantation. N@C60 is soluble in organic solvents and stable in air. A special feature is that it gives a very clear hyperfine split EPR signal with sharp lines even in the solid. This makes it an ideal probe for monitoring chemical reactions of C60 via changes of the EPR signal. As an example, the formation of the monoadduct of diethyl malonate on C60 will be discussed. In general, N@C60 can be used as a probe or tracer for monitoring reactions or the transport of C60. We show that C60 is an ideal trap for atomic nitrogen. Nitrogen is in the center of C60 and keeps its atomic structure. In a first experiment, the vibrations of nitrogen in C60 were studied.
BLDSC reference no.: D236503. Supervisors: Andrew Briggs, Arzhang Ardavan. Thesis (D.Phil.)--University of Oxford, 2005. Includes bibliography.
We report the purification of the nitrogen-containing incar-fullerenes iNC(60) and iNC(70), and their characterisation by UV-Vis absorption spectroscopy.
We examine the temperature dependence of the electron spin relaxation times of the molecules N@C60 and N@C70 (which comprise atomic nitrogen trapped within a carbon cage) in liquid CS2 solution. The results are inconsistent with the fluctuating zero-field splitting (ZFS) mechanism, which is commonly invoked to explain electron spin relaxation for S> or =1 spins in liquid solution, and is the mechanism postulated in the literature for these systems. Instead, we find an Arrhenius temperature dependence for N@C60 , indicating the spin relaxation is driven primarily by an Orbach process. For the asymmetric N@C70 molecule, which has a permanent ZFS, we resolve an additional relaxation mechanism caused by the rapid reorientation of its ZFS. We also report the longest coherence time (T2) ever observed for a molecular electron spin, being 0.25 ms at 170 K.
The application of frequency control and timing devices in modern military electronics systems is reviewed. The manner in which the stability and accuracy of these devices impact the performance of military communication, navigation, surveillance, electronic warfare, missile guidance, and identification-friend-or-foe (IFF) systems is discussed.< >
We examine environmental effects of surrounding nuclear spins on the electron spin relaxation of the N@C60 molecule (which consists of a nitrogen atom at the centre of a fullerene cage). Using dilute solutions of N@C60 in regular and deuterated toluene, we observe and model the effect of translational diffusion of nuclear spins of the solvent molecules on the N@C60 electron spin relaxation times. We also study spin relaxation in frozen solutions of N@C60 in CS2, to which small quantities of a glassing agent, S2Cl2 are added. At low temperatures, spin relaxation is caused by spectral diffusion of surrounding nuclear 35Cl and 37Cl spins in the S2Cl2, but nevertheless, at 20 K, T2 times as long as 0.23 ms are observed. Comment: 7 pages, 6 figures
Half-Title PageTitle PageCopyright PageDedication PageContentsPreface
In this article, the production and the properties of endohedral fullerenes N@C60, P@C60 and N@C70 are described. The distinct feature of these systems is that the enclosed nitrogen and phosphorous atoms keep their atomic ground state configuration and are localized in the center of the fullerenes. The atoms are almost freely suspended in these molecular cages and exhibit properties resembling those of ions in electromagnetic traps, i.e. sharp spectroscopic transitions and long life times. Since the fullerene shell can be easily manipulated, a large variety of different physical or chemical modifications can be realized.
Quantum computing is an emerging area within the information sciences revolving around the concept of quantum bits (qubits). A major obstacle is the extreme fragility of these qubits due to interactions with their environment that destroy their quantumness. This phenomenon, known as decoherence, is of fundamental interest. There are many competing candidates for qubits, including superconducting circuits, quantum optical cavities, ultracold atoms and spin qubits, and each has its strengths and weaknesses. When dealing with spin qubits, the strongest source of decoherence is the magnetic dipolar interaction. To minimize it, spins are typically diluted in a diamagnetic matrix. For example, this dilution can be taken to the extreme of a single phosphorus atom in silicon, whereas in molecular matrices a typical ratio is one magnetic molecule per 10,000 matrix molecules. However, there is a fundamental contradiction between reducing decoherence by dilution and allowing quantum operations via the interaction between spin qubits. To resolve this contradiction, the design and engineering of quantum hardware can benefit from a ‘bottom-up’ approach whereby the electronic structure of magnetic molecules is chemically tailored to give the desired physical behaviour. Here we present a way of enhancing coherence in solid-state molecular spin qubits without resorting to extreme dilution. It is based on the design of molecular structures with crystal field ground states possessing large tunnelling gaps that give rise to optimal operating points, or atomic clock transitions, at which the quantum spin dynamics become protected against dipolar decoherence. This approach is illustrated with a holmium molecular nanomagnet in which long coherence times (up to 8.4 microseconds at 5 kelvin) are obtained at unusually high concentrations. This finding opens new avenues for quantum computing based on molecular spin qubits.
In this paper, we present a fully-integrated receiver for NMR microscopy applications manufactured in a 0.13 μm CMOS technology. The design co-integrates a 10-turn planar detection coil together with a complete quadrature, low-IF downconversion receiver on a single chip, which operates from a single 1.5 V supply with a total power dissipation of 18 mW. The detector’s measured time-domain spin sensitivity is at 7 T. Additionally, the paper discusses two important aspects of NMR microscopy using planar detection coils: the link between the detection coil’s spin sensitivity and the achievable image SNR and the correction of image artifacts induced by the inhomogeneous sensitivity profile of planar detection coils. More specifically, we derive analytical expressions for both the theoretical image SNR as a function of the coil’s spin sensitivity and the sensitivity correction for a known coil sensitivity profile in CTI MR imaging experiments. Both expressions are validated using measured data in the imaging section of the paper. Thanks to the improved spin sensitivity of the utilized integrated receiver chip compared to a previously presented design, we were able to obtain sensitivity corrected images in a 7 T spectroscopy magnet with isotropic resolutions of 9.6 μm and 5 μm with single-shot SNRs of 37 and 15 in relatively short imaging times of 4.4 h and 24 h, respectively.
We report the purification of the nitrogen-containing incarfullerenes iNC(60) and iNC(70), and their characterisation by UV-Vis absorption spectroscopy.
1. Elements of Resonance.- 2 Basic Theory.- 3. Magnetic Dipolar Broadening of Rigid Lattices.- 4. Magnetic Interactions of Nuclei with Electrons.- 5. Spin-Lattice Relaxation and Motional Narrowing of Resonance Lines.- 6. Spin Temperature in Magnetism and in Magnetic Resonance.- 7. Double Resonance.- 8. Advanced Concepts in Pulsed Magnetic Resonance.- 9. Multiple Quantum Coherence.- 10. Electric Quadrupole Effects.- 11. Electron Spin Resonance.- 12. Summary.- Problems.- Appendixes.- A. A Theorem About Exponential Operators.- B. Some Further Expressions for the Susceptibility.- D. A Theorem from Perturbation Theory.- E. The High Temperature Approximation.- F. The Effects of Changing the Precession Frequency - Using NMR to Study Rate Phenomena.- G. Diffusion in an Inhomogeneous Magnetic Field.- H. The Equivalence of Three Quantum Mechanics Problems.- I. Powder Patterns.- J. Time-Dependent Hamiltonians.- K. Correction Terms in Average Hamiltonian Theory - The Magnus Expansion.- Selected Bibliography.- References.- Author Index.
Frequency standards based on atomic states, such as Rb or Cs vapors, or single-trapped ions, are the most precise measures of time. Here we propose and analyze a precision oscillator approach based upon spins in a solid-state system, in particular, the nitrogen-vacancy defect in single-crystal diamond. We show that this system can have stability approaching portable atomic standards and is readily incorporable as a chip-scale device. Using a pulsed spin-echo technique, we anticipate an Allan deviation of σy=10−7τ−1/2 limited by thermally-induced strain variations; in the absence of such thermal fluctuations, the system is limited by spin dephasing and harbors an Allan deviation nearing ∼10−12τ−1/2. Potential improvements based upon advanced diamond material processing, temperature stabilization, and nanophotonic engineering are discussed.
Measurements of paramagnetic resonance absorption at room temperature in single crystals of potassium chrome alum and ammonium chrome alum made at a frequency of 9375 mc/sec. are described. The method makes use of a magic-T bridge with a low level crystal detector which essentially measures the magnetic susceptibility. Data are given for three orientations of the crystals for both the diluted and undiluted salts. The Stark splitting and the g factor of the ground state are evaluated from the positions of the absorption peaks. The theory which is used for the computation of the Stark splitting is extended to include the (110) orientation.
The room temperature solubility of pure C[sub 60] has been determined in 47 solvents. The solubilities cover a wide range, from 0.01 mg/mL in methanol to 50 mg/mL in 1-chloronaphthalene. The solubilities in CS[sub 2], toluene, and hexane, three of the commonly employed solvents, are 7.9, 2.8, and 0.04 mg/mL, respectively. An examination of the solubilities of C[sub 60] as a function of the solvent properties such as index of refraction, dielectric constant, molecular size, Hildebrand solubility parameter, and H-bonding strength reaffirms the century-old principle like dissolves like. No single solvent parameter can uniformly predict the solubility of C[sub 60], but a composite picture of solvents with high solubility for C[sub 60] emerges: large index of refraction, dielectric constant around 4, large molecular volume, Hildebrand solubility parameter equal to 10 cal[sup 1/2] cm[sup [minus]3/2], and tendency to act as a moderate strength nucleophile. 18 refs., 4 figs., 1 tab.
This paper presents the latest progress in the development, fabrication, and characterization of microfabricated atomic frequency references at NIST. With volumes below 10 mm3 the physics packages contain the complete integrated assembly for probing the ground-state hyperfine splitting frequency of the alkali atoms by coherent population trapping (CPT). This technique allows for a simple and compact device containing a vertical-cavity surface-emitting laser (VCSEL), optics to shape the laser beam, a vapor cell containing the atoms, and a detector. We present an improved technique for microfabricating the miniature alkali vapor cells. When integrated into a CPT clock, a clear reduction of long-term frequency drifts is observed. This leads to a fractional frequency instability of less than 10-11 at one hour of integration, a more than one order of magnitude improvement over previous results. We identify the remaining sensitivities of the clock frequency to environmental influences and propose ways to reduce them.
The double resonance spectra of N14 and N15 ammonium ion are in good agreement with the spectra calculated with a Hamiltonian that is made stationary by transformation to a rotating coordinate system. No effects of cross relaxation are apparent. Terms in the interaction of the strong radio frequency field with the proton magnetic moment, and off‐diagonal elements in the nitrogen‐proton spin‐spin coupling can be neglected. The effects of sweeping magnetic field rather than frequency permit a very accurate measurement of the nitrogen resonance frequency, and the ratio of the N15 and N14 magnetogyric ratios.
Fullerenes, C60 and C70, are ideal containers for atomic nitrogen. We will show by electron paramagnetic resonance (EPR) experiments that nitrogen in C60 keeps its atomic ground state configuration and resides in the center of the cage. This is the first time that atomic nitrogen is stabilized at ambient conditions. The inert shell of the fullerene protects the highly reactive nitrogen from undergoing chemical reactions with the surroundings. The fullerene cage is the chemical analogue of the Faraday cage in case of electrical fields, i.e. it shields off the chemical reactivity. As for the free nitrogen atom, the spins of the three p-electrons of nitrogen in C60 are parallel (S = 3/2) and the atom has spherical symmetry. Due to the center position of nitrogen in C60, extremely sharp EPR lines are observed. This reflects the absence of a strong host–guest interaction and shows that the individuality of nitrogen in the fullerenes is preserved. Further evidence for the almost interaction-free suspension of nitrogen in the fullerene cages is provided by g-factor measurements. These investigations show that magnetic shielding of the host molecules can account for the observed differences between N@C60 and N@C70. The fullerene cage can be chemically modified without destroying the endohedral complex. The chemical modifications change the symmetry of the molecule which is observed through an additional fine structure in the EPR spectrum. Influences of the modifications on the stability of N@C60 will be discussed.
This paper describes a new class of frequency
reference. The frequency source uses the same operating
principle as a passive atomic frequency standard; however, the device is entirely solid-state, removing many cost and
reliability issues associated with gas phase atomic clocks. More specifically, the "atomic resonance" is derived from zero-field magnetic resonance transitions of the vanadium ion in magnesium oxide. The characteristics of these resonances will be described in detail. The apparatus for measuring the "atomic" resonances uses a microwave resonant cavity and frequency-discriminator circuit. Using integrated circuits, the radio-frequency signal processing functions can be implemented at very low cost in a reliable manufacturing process. We discuss the system design and the measurement sensitivity. The estimated short term stability is in the range of 10^(-8) to 10^(-9) @ 1 s. Advantages of the new frequency reference may include immunity to vibration, reduced aging compared to crystal oscillators, and immediate cold start.
The table is a compilation of experimental measurements of static magnetic dipole and electric quadrupole moments of ground states and excited states of atomic nuclei throughout the periodic table. To aid identification of the states, their excitation energy, half-life, spin, and parity are given, along with a brief indication of the method and any reference standard used in the particular measurement. The literature search covers the period to late 2004. Many of the entries prior to 1988 follow those in Raghavan [At. Data Nucl. Data Tables 42 (1989) 189].
A fresh approach to the calculation of signal-to-noise ratio, using the Principle of Reciprocity, is formulated. The method is shown, for a solenoidal receiving coil, to give the same results as the traditional method of calculation, but its advantage lies in its ability to predict the ratio for other coil configurations. Particular attention is paid to the poor performance of a saddle-shaped (or Helmholtz) coil. Some of the practical problems involved are also discussed, including the error of matching the probe to the input impedance of the preamplifier.
We present a discussion of recent concepts for the construction of a spin quantum computer using endohedral fullerenes. The fullerene molecule is a static, room-temperature trap for atoms with slowly relaxing electron and nuclear spins. The fullerene containers can be used to arrange the spins in complex structures such as a linear chain, to form a spin quantum register. We discuss the probable properties of such registers and different strategies to use them in a quantum computer design, including gating and read-out methods.
A new paramagnetic defect in solid C60 was produced by nitrogen implantation in solid C60. The hyperfine splitting and the isotope effect unambiguously show that the paramagnetic center contains one nitrogen nucleus. The hyperfine interaction is isotropic, its value is comparable to that of the free nitrogen atom, and the spin of the electron system is S = 3/2, as in atomic nitrogen. The complex responsible for this center is soluble in toluene and CS2 and is stable. We suggest that the complex consists of nitrogen inside C60.
Time domain methods for characterizing the performance of precision
clocks and oscillators are reviewed, and it is shown that classical
statistics do not allow characterization of common kinds of random
signal variations noted in precision oscillators. It is found that the
two-sample Allan variance provides a valuable and convergent measure of
the power-law spectral-density models which are useful in the
characterization of such random deviations. Once these deviations are
characterized, optimum time and frequency estimates can be obtained, and
near-optimum systematic effects (which often cause the predominant time
and frequency deviations) can be estimated.
A simple method to produce a clock transition with purely optical
means by modulated pumping is described. The field-independent ground
state resonance of 87Rb atoms using sinusoidal modulation of
the injection current of an AlGaAs laser diode emitting at 780 nm (FM
modulation) is observed. The 6.835 GHz resonance with a subharmonic
modulation frequency of 1.139 GHz is detected. A high-contrast resonance
peak is observed and a condition for zero light shift is found. The
linewidth is 3 kHz (at 6.835 GHz) in this preliminary experiment, due to
the small size of the light beam (~2 mm diameter) and the low buffer gas
pressure (680 Pa) that was used. A theoretical model that explains the
main features of the experiment is described
A theoretical proposal for reducing an entire atomic clock to micron dimensions. A phosphorus or nitrogen atom is introduced into a fullerene cage. This endohedral fullerene is then coated with an insulating shell and a number of them are deposited as a thin layer on a silicon chip. Next to this layer a GMR sensor is fabricated which is close to the endohedral fullerenes. This GMR sensor measures oscillating magnetic fields on the order of micro-gauss from the nuclear spins varying at the frequency of the hyperfine transition (413 MHz frequency). Given the micron scale and simplicity of this system only a few transistors are needed to control the waveforms and to perform digital clocking. This new form of atomic clock exhibits extremely low power (nano watts), high vibration and shock resistance, stability on the order of 10^{-9}, and is compatible with MEMS fabrication and chip integration. As GMR sensors continue to improve in sensitivity the stability of this form of atomic clock will increase proportionately.
Le Roy for assistance with sample preparation We acknowledge DSTL, EPSRC (EP
- J Wedge
J. Wedge for useful discussions, and J. J. Le Roy
for assistance with sample preparation. We acknowledge DSTL, EPSRC (EP/J015067/1, EP/K030108/1,
EP/N014995/1, EP/P511377/1), the Royal Academy of
Engineering, a Marie Curie CIG award, and LocatorX
Inc. of Jackson Beach, Florida.
45s CSAC chip scale atomic clock, Microsemi Corporation
- T M Quantum
- Sa
Quantum TM SA.45s CSAC chip scale atomic clock, Microsemi Corporation, Aliso Viejo, California, USA (2017).
- J. Vanier
The chip-scale atomic clock-prototype evaluation
- R Lutwak
- A Rashed
- M Varghese
- G Tepolt
- J Leblanc
- M Mescher
- D K Serkland
- K M Geib
- G M Peake
- S Römisch
R. Lutwak, A. Rashed, M. Varghese, G. Tepolt, J. LeBlanc,
M. Mescher, D. K. Serkland, K. M. Geib, G. M. Peake, and
S. Römisch, The chip-scale atomic clock-prototype evaluation, in Proceedings of the 39th Annual Precise Time and
Time Interval Systems and Applications Meeting (Institute
of Navigation, Manassas, USA, 2007) pp. 269-290.
- B Pietzak
- M Waiblinger
- T Almeida Murphy
- A Weidinger
- M Höhne
- E Dietel
- A Hirsch
B. Pietzak, M. Waiblinger, T. Almeida Murphy, A. Weidinger,
M. Höhne, E. Dietel, and A. Hirsch, Properties of endohedral
N@C 60, Carbon 36, 613 (1998).
for a derivation of the observed lineshape and fitting procedures
See Supplemental Material at http://link.aps.org/
supplemental/10.1103/PhysRevLett.119.140801 for a derivation of the observed lineshape and fitting procedures.
- E C Hannah
- M A Brown
E. C. Hannah and M. A. Brown, Conceptual design of a
micron-scale atomic clock, arXiv:0707.4624.
The signal-to-noise ratio of the nuclear magnetic resonance experiment
- D I Hoult
- R E Richards
D. I. Hoult and Richards R. E., "The signal-to-noise ratio
of the nuclear magnetic resonance experiment," Journal of
Magnetic Resonance (1969) 24, 71 -85 (1976).