Magnetic resonance imaging (MRI) has revolutionized biomedical science by providing non-invasive, three-dimensional biological imaging. However, spatial resolution in conventional MRI systems is limited to tens of micrometres, which is insufficient for imaging on molecular scales. Here, we demonstrate an MRI technique that provides subnanometre spatial resolution in three dimensions, with single electron-spin sensitivity. Our imaging method works under ambient conditions and can measure ubiquitous 'dark' spins, which constitute nearly all spin targets of interest. In this technique, the magnetic quantum-projection noise of dark spins is measured using a single nitrogen-vacancy (NV) magnetometer located near the surface of a diamond chip. The distribution of spins surrounding the NV magnetometer is imaged with a scanning magnetic-field gradient. To evaluate the performance of the NV-MRI technique, we image the three-dimensional landscape of electronic spins at the diamond surface and achieve an unprecedented combination of resolution (0.8 nm laterally and 1.5 nm vertically) and single-spin sensitivity. Our measurements uncover electronic spins on the diamond surface that can potentially be used as resources for improved magnetic imaging. This NV-MRI technique is immediately applicable to diverse systems including imaging spin chains, readout of spin-based quantum bits, and determining the location of spin labels in biological systems.

Magnetic skyrmions are two-dimensional non-collinear spin textures characterized by an integer topological number. Room-temperature skyrmions were recently found in magnetic multilayer stacks, where their stability was largely attributed to the interfacial Dzyaloshinskii–Moriya interaction. The strength of this interaction and its role in stabilizing the skyrmions is not yet well understood, and imaging of the full spin structure is needed to address this question. Here, we use a nitrogen-vacancy centre in diamond to measure a map of magnetic fields produced by a skyrmion in a magnetic multilayer under ambient conditions. We compute the manifold of candidate spin structures and select the physically meaningful solution. We find a Néel-type skyrmion whose chirality is not left-handed, contrary to preceding reports. We propose skyrmion tube-like structures whose chirality rotates through the film thickness. We show that NV magnetometry, combined with our analysis method, provides a unique tool to investigate this previously inaccessible phenomenon.

We perform Landau-Zener-Stückelberg interferometry on a single electron GaAs charge qubit by repeatedly driving the system through an avoided crossing. We observe coherent destruction of tunneling, where periodic driving with specific amplitudes inhibits current flow. We probe the quantum dot occupation using a charge detector, observing oscillations in the qubit population resulting from the microwave driving. At a frequency of 9 GHz we observe excitation processes driven by the absorption of up to 17 photons. Simulations of the qubit occupancy are in good agreement with the experimental data.PACS numbers: 73.21. La, 73.63.Kv, 85.35.Be, 85.35.Ds Semiconductor quantum dots are fruitful systems for exploring phenomena arising from quantum interference effects [1][2][3][4][5][6]. Landau-Zener-Stückelberg (LZS) interferometry has recently emerged as a novel way to study quantum coherence in solid state systems. LZS theory was initially described in the context of atomic collisions and relies on having an effective two-level system with an avoided crossing in the energy level spectrum [7][8][9][10][11]. Repeated sweeps through the avoided crossing result in successive Landau-Zener transitions, allowing control of the final state probability. While the theory was initially applied to atomic collisions, recent advances in the fabrication of solid state quantum devices have made it experimentally accessible in a wide variety of systems, ranging from superconducting qubits [12] to nitrogen vacancy centers in diamond [13,14]. In superconducting qubits, LZS interferometry has been used with great success to determine the energy level diagram and to measure qubit coherence times [12,15,16]. In spin qubits, LZS interferometry has been harnessed to drive coherent singlet-triplet transitions resulting in spin rotations that are much faster than those obtained using conventional electron spin resonance [17,18].In this Rapid Communication we perform LZS interferometry on a single electron GaAs double quantum dot (DQD) charge qubit. The sample geometry is illustrated in the scanning electron microscope (SEM) image shown in Fig. 1(a). Ti/Au gate electrodes are fabricated on top of a GaAs/AlGaAs heterostructure that is grown using molecular beam epitaxy. The gate electrodes selectively deplete regions of the two-dimensional electron gas located 110 nm below the surface of the wafer, forming a DQD containing a single electron. In this experiment, a third dot is used as a charge detector, which allows non-invasive measurements of the charge state occupancy [19]. A fixed 100 mT field is applied perpendicular to the plane of the sample. Despite their simplicity, charge qubits are of great experimental importance as they allow for direct quantum control through electric fields, with coherent control rates dictated by tunnel couplings that can easily approach 10 GHz. They also serve as building blocks for more complex quantum systems, such as spin qubits [20].We focus on the one electron regime, where the DQD contains a single charge...

We demonstrate multipulse quantum control of a single electron charge qubit. The qubit is manipulated by applying nonadiabatic voltage pulses to a surface depletion gate and readout is achieved using a quantum point contact charge sensor. We observe Ramsey fringes in the excited state occupation in response to a pi/2 - pi/2 pulse sequence and extract T2* ~ 60 ps away from the charge degeneracy point. Simulations suggest these results may be extended to implement a charge-echo by reducing the interdot tunnel coupling and pulse rise time, thereby increasing the nonadiabaticity of the pulses.Comment: Related papers at http://pettagroup.princeton.ed

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