Pengfei Wang

Single-protein spin resonance spectroscopy under ambient conditions

Single-protein spectroscopy The spin of a single nitrogen-vacancy (NV) center in diamond is a highly sensitive magnetic-field sensor. Shi et al. used the NV center to detect a nitroxidelabeled protein through electron spin resonance under ambient conditions (see the Perspective by Hemmer and Gomes). The strength of the interaction and the details of the hyperfine interaction between the electron and nitrogen spin revealed the position and orientation of the spin label relative to the NV center. The findings also elucidate the dynamical motions of the protein on the diamond surface. Science, this issue p. 1135; see also p. 1072 Electron spin resonance (ESR) signals from a single labeled protein were detected with diamond nitrogen-vacancy centers. [Also see Perspective by Hemmer and Gomes] Magnetic resonance is essential in revealing the structure and dynamics of biomolecules. However, measuring the magnetic resonance spectrum of single biomolecules has remained an elusive goal. We demonstrate the detection of the electron spin resonance signal from a single spin-labeled protein under ambient conditions. As a sensor, we use a single nitrogen vacancy center in bulk diamond in close proximity to the protein. We measure the orientation of the spin label at the protein and detect the impact of protein motion on the spin label dynamics. In addition, we coherently drive the spin at the protein, which is a prerequisite for studies involving polarization of nuclear spins of the protein or detailed structure analysis of the protein itself.

Sensing and atomic-scale structure analysis of single nuclear-spin clusters in diamond

Being able to sense nuclear spin dimers is an important next step towards single-molecule structural analysis from NMR measurements. Now the sensing of a single 13C–13C nuclear spin dimer near a nitrogen–vacancy centre in diamond is reported, together with a structural characterization at atomic-scale resolution.

Coherence-protected quantum gate by continuous dynamical decoupling in diamond.

In order to achieve reliable quantum-information processing results, we need to protect quantum gates along with the qubits from decoherence. Here we demonstrate experimentally on a nitrogen-vacancy system that by using a continuous-wave dynamical decoupling method, we might not only prolong the coherence time by about 20 times but also protect the quantum gates for the duration of the controlling time. This protocol shares the merits of retaining the superiority of prolonging the coherence time and at the same time easily combining with quantum logic tasks. This method can be useful in tasks where the duration of quantum controlling exceeds far beyond the dephasing time.

Observation of an anomalous decoherence effect in a quantum bath at room temperature

The decoherence of quantum objects is a critical issue in quantum science and technology. It is generally believed that stronger noise causes faster decoherence. Strikingly, recent theoretical work suggests that under certain conditions, the opposite is true for spins in quantum baths. Here we report an experimental observation of an 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 theoretical results confirms the controllability of the weakly coupled nuclear spins in the bath, which is useful in quantum information processing and quantum metrology.

High-resolution vector microwave magnetometry based on solid-state spins in diamond

The measurement of the microwave field is crucial for many developments in microwave technology and related applications. However, measuring microwave fields with high sensitivity and spatial resolution under ambient conditions remains elusive. In this work, we propose and experimentally demonstrate a scheme to measure both the strength and orientation of the microwave magnetic field by utilizing the quantum coherent dynamics of nitrogen vacancy centres in diamond. An angular resolution of 5.7u2009mrad and a sensitivity of 1.0u2009μTu2009Hz−1/2 are achieved at a microwave frequency of 2.6000u2009GHz, and the microwave magnetic field vectors generated by a copper wire are precisely reconstructed. The solid-state microwave magnetometry with high resolution and wide frequency range that can work under ambient conditions proposed here enables unique potential applications over other state-of-art microwave magnetometry.

Demonstration of motion transduction based on parametrically coupled mechanical resonators.

Universal sensing of the motion of mechanical resonators with high precision and low backaction is of paramount importance in ultraweak signal detection, which plays a fundamental role in modern physics. Here we present a universal scheme that mechanically transfers the motion of the resonator not directly measurable to the one that can be precisely measured using mechanical frequency conversion. Demonstration of the scheme at room temperature shows that both the motion imprecision and the backaction force are below the intrinsic level of the objective resonator, which agrees well with our theoretical prediction. The scheme developed here provides an effective interface between an arbitrary mechanical resonator and a high quantum efficient displacement sensor, and is expected to find extensive applications in highly demanding mechanical-based force measurements.

Direct Measurement of Topological Numbers with Spins in Diamond

Topological numbers can characterize the transition between different topological phases, which are not described by Landaus paradigm of symmetry breaking. Since the discovery of the quantum Hall effect, more topological phases have been theoretically predicted and experimentally verified. However, it is still an experimental challenge to directly measure the topological numbers of various predicted topological phases. In this Letter, we demonstrate quantum simulation of topological phase transition of a quantum wire (QW), by precisely modulating the Hamiltonian of a single nitrogen-vacancy (NV) center in diamond. Deploying a quantum algorithm of finding eigenvalues, we reliably extract both the dispersion relations and topological numbers. This method can be further generalized to simulate more complicated topological systems.

High-Time-Resolution Nuclear Magnetic Resonance With Nitrogen-Vacancy Centers

We present a field-programmable gate array (FPGA)-based solution for high-time-resolution nanoscale nuclear magnetic resonance, with nitrogen-vacancy centers as a probe. The Xilinx FPGA is used to implement a high-performance pulse generator, which contributes to high-precision measurement for the nuclear magnetic resonance (NMR) signal. The pulse generator outputs continuous pulses with a time resolution of 50 ps and a dynamic range of 5 ns to 2.68 s. The central control and the readout logics for the NMR experiment are fully implemented in the FPGA. We observed nanoscale NMR signals of hydrogen atoms by measuring the period of the Larmor precession with a 50 ps time resolution. Furthermore, we demonstrate the ability to distinguish signals of adjacent frequencies, which is a great advantage in high-resolution analysis for the nanoscale NMR.

Searching for an exotic spin-dependent interaction with a single electron-spin quantum sensor

Searching for new particles beyond the standard model is crucial for understanding several fundamental conundrums in physics and astrophysics. Several hypothetical particles can mediate exotic spin-dependent interactions between ordinary fermions, which enable laboratory searches via the detection of the interactions. Most laboratory searches utilizexa0a macroscopic source and detector, thus allowing the detection of interactions with submillimeter force range and above. It remains a challenge to detect the interactions at shorter force ranges. Here we propose and demonstrate that a near-surface nitrogen-vacancy center in diamond can be utilized as a quantum sensor to detect the monopole–dipole interaction between an electron spin and nucleons. Our result sets a constraint for the electron–nucleon coupling,