The development of highly sensitive and rapid biosensing tools targeted to the highly contagious virus SARS-CoV-2 is critical to tackling the COVID-19 pandemic. Quantum sensors can play an important role because of their superior sensitivity and fast improvements in recent years. Here we propose a molecular transducer designed for nitrogen-vacancy (NV) centers in nanodiamonds, translating the presence of SARS-CoV-2 RNA into an unambiguous magnetic noise signal that can be optically read out. We evaluate the performance of the hybrid sensor, including its sensitivity and false negative rate, and compare it to widespread diagnostic methods. The proposed method is fast and promises to reach a sensitivity down to a few hundreds of RNA copies with false negative rate less than 1%. The proposed hybrid sensor can be further implemented with different solid-state defects and substrates, generalized to diagnose other RNA viruses, and integrated with CRISPR technology.
Sensing local environment through the motional response of small molecules lays the foundation of many fundamental technologies. The information of local viscosity, for example, is contained in the random rotational Brownian motions of molecules. However, detection of the motions is challenging for molecules with sub-nanometer scale or high motional rates. Here we propose and experimentally demonstrate a novel method of detecting fast rotational Brownian motions of small magnetic molecules. With electronic spins as sensors, we are able to detect changes in motional rates, which yield different noise spectra and therefore different relaxation signals of the sensors. As a proof-of-principle demonstration, we experimentally implemented this method to detect the motions of gadolinium (Gd) complex molecules with nitrogen-vacancy (NV) centers in nanodiamonds. With all-optical measurements of the NV centers' longitudinal relaxation, we distinguished binary solutions with varying viscosities. Our method paves a new way for detecting fast motions of sub-nanometer sized magnetic molecules with better spatial resolution than conventional optical methods. It also provides a new tool in designing better contrast agents in magnetic resonance imaging. * pcappell@mit.edu arXiv:1907.05396v1 [quant-ph]
Magnetic monopoles play a central role in areas of physics that range from electromagnetism to topological matter. String theory promotes conventional vector gauge fields of electrodynamics to tensor gauge fields and predicts the existence of more exotic tensor monopoles. Here, we report the synthesis of a tensor monopole in a four-dimensional parameter space defined by the spin degrees of freedom of a single solid-state defect in diamond. Using two complementary methods, we characterized the tensor monopole by measuring its quantized topological charge and its emanating Kalb-Ramond field. By introducing a fictitious external field that breaks chiral symmetry, we further observed an intriguing spectral transition, characterized by spectral rings protected by mirror symmetries. Our work demonstrates the possibility of emulating exotic topological structures inspired by string theory.
Solid-state spins such as nitrogen-vacancy (NV) center are promising platforms for large-scale quantum networks. Despite the optical interface of NV center system, however, the significant attenuation of its zero-phonon-line photon in optical fiber prevents the network extended to long distances. Therefore a telecom-wavelength photon interface would be essential to reduce the photon loss in transporting quantum information. Here we propose an efficient scheme for coupling telecom photon to NV center ensembles mediated by rare-earth doped crystal. Specifically, we proposed protocols for high fidelity quantum state transfer and entanglement generation with parameters within reach of current technologies. Such an interface would bring new insights into future implementations of long-range quantum network with NV centers in diamond acting as quantum nodes. IntroductionQuantum network based on solid-state quantum memories are a promising platform for long range quantum communication and remote sensing [1][2][3]. Quantum nodes in a network require robust storage, high fidelity and efficient interface to achieve these demanding applications. Among many physical platforms, nitrogen vacancy (NV) centers stand out for their very long coherence time in the ground states, making them ideal systems to be used as stationary nodes for quantum computer or sensor networks. Microwave and optical interfaces have provided the NV system with a flexible toolset of control knobs, as required in many emerging technologies. This has enabled a recent demonstration of deterministic entanglement generation between two NV centers in diamond [4] with an entanglement rate of about 40 Hz. Despite these successes, NV centers present some shortcomings for quantum communication applications: the NV spin has a zero phonon line (ZPL) at 637 nm and it only corresponds to 3% of the total emission.The propagation loss in optical fibers at this wavelength (8 dB/km) is much larger compared with telecommunication ranges (less than 0.2 dB/km). To extend the entanglement generation scheme to large distance would thus benefit from using a telecom photon interface. The conventional way to overcome this limit is to perform parametric down conversion to convert the photons into telecom-wavelength photons (tele-photons), as demonstrated in several systems including quantum dots [5][6][7], trapped ions [8-10] and atomic ensembles [11][12][13].The low emission rate into the ZPL limits the rate of entanglement generation. The emission fraction into the ZPL could be enhanced by a microcavity via the Purcell effect [14], while a difference frequency generation, used in recent experiments, achieved conversion of single NV photons into telecom wavelength with 17% efficiency [15,16]. However, the signal-to-noise ratio was limited by pump-induced noise in the conversion process [17,18] and resonance driving at cryogenic temperature is required, preventing room temperature applications.An alternative approach is to work with the microwave interface of NV centers and then ...
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