Temperature-Dependent Spin-Lattice Relaxation of the Nitrogen-Vacancy Spin Triplet in Diamond.

Spin-lattice relaxation within the nitrogen-vacancy (NV) center's electronic ground-state spin triplet limits its coherence times, and thereby impacts its performance in quantum applications. We report measurements of the relaxation rates on the NV center's |m_{s}=0⟩↔|m_{s}=±1⟩ and |m_{s}=-1⟩↔|m_{s}=+1⟩ transitions as a function of temperature from 9 to 474 K in high-purity samples. We show that the temperature dependencies of the rates are reproduced by an ab initio theory of Raman scattering due to second-order spin-phonon interactions, and we discuss the applicability of the theory to other spin systems. Using a novel analytical model based on these results, we suggest that the high-temperature behavior of NV spin-lattice relaxation is dominated by interactions with two groups of quasilocalized phonons centered at 68.2(17) and 167(12) meV.

One- and Two-Dimensional Nuclear Magnetic Resonance Spectroscopy with a Diamond Quantum Sensor.

We report on Fourier spectroscopy experiments performed with near-surface nitrogen-vacancy centers in a diamond chip. By detecting the free precession of nuclear spins rather than applying a multipulse quantum sensing protocol, we are able to unambiguously identify the NMR species devoid of harmonics. We further show that, by engineering different Hamiltonians during free precession, the hyperfine coupling parameters as well as the nuclear Larmor frequency can be selectively measured with up to five digits of precision. The protocols can be combined to demonstrate two-dimensional Fourier spectroscopy. Presented techniques will be useful for mapping nuclear coordinates in molecules deposited on diamond sensor chips, en route to imaging their atomic structure.

Probing the dynamics of a nuclear spin bath in diamond through time-resolved central spin magnetometry.

Using fast electron spin resonance spectroscopy of a single nitrogen-vacancy defect in diamond, we demonstrate real-time readout of the Overhauser field produced by its nuclear spin environment under ambient conditions. These measurements enable narrowing the Overhauser field distribution by postselection, corresponding to a conditional preparation of the nuclear spin bath. Correlations of the Overhauser field fluctuations are quantitatively inferred by analyzing the Allan deviation over consecutive measurements. This method allows us to extract the dynamics of weakly coupled nuclear spins of the reservoir.

Nanoscale magnetic sensing with an individual electronic spin in diamond.

Detection of weak magnetic fields with nanoscale spatial resolution is an outstanding problem in the biological and physical sciences. For example, at a distance of 10 nm, the spin of a single electron produces a magnetic field of about 1 muT, and the corresponding field from a single proton is a few nanoteslas. A sensor able to detect such magnetic fields with nanometre spatial resolution would enable powerful applications, ranging from the detection of magnetic resonance signals from individual electron or nuclear spins in complex biological molecules to readout of classical or quantum bits of information encoded in an electron or nuclear spin memory. Here we experimentally demonstrate an approach to such nanoscale magnetic sensing, using coherent manipulation of an individual electronic spin qubit associated with a nitrogen-vacancy impurity in diamond at room temperature. Using an ultra-pure diamond sample, we achieve detection of 3 nT magnetic fields at kilohertz frequencies after 100 s of averaging. In addition, we demonstrate a sensitivity of 0.5 muT Hz(-1/2) for a diamond nanocrystal with a diameter of 30 nm.

Single-shot readout of multiple nuclear spin qubits in diamond under ambient conditions.

We use the electronic spin of a single nitrogen-vacancy defect in diamond to observe the real-time evolution of neighboring single nuclear spins under ambient conditions. Using a diamond sample with a natural abundance of (13)C isotopes, we first demonstrate high fidelity initialization and single-shot readout of an individual (13)C nuclear spin. By including the intrinsic (14)N nuclear spin of the nitrogen-vacancy defect in the quantum register, we then report the simultaneous observation of quantum jumps linked to both nuclear spin species, providing an efficient initialization of the two qubits. These results open up new avenues for diamond-based quantum information processing including active feedback in quantum error correction protocols and tests of quantum correlations with solid-state single spins at room temperature.

Environment-assisted precision measurement.

We describe a method to enhance the sensitivity of precision measurements that takes advantage of the environment of a quantum sensor to amplify the response of the sensor to weak external perturbations. An individual qubit is used to sense the dynamics of surrounding ancillary qubits, which are in turn affected by the external field to be measured. The resulting sensitivity enhancement is determined by the number of ancillas that are coupled strongly to the sensor qubit; it does not depend on the exact values of the coupling strengths and is resilient to many forms of decoherence. The method achieves nearly Heisenberg-limited precision measurement, using a novel class of entangled states. We discuss specific applications to improve clock sensitivity using trapped ions and magnetic sensing based on electronic spins in diamond.

Structural characterization of the saxitoxin-targeting APTSTX1 aptamer using optical tweezers and molecular dynamics simulations.

Optical tweezers have enabled the exploration of picoNewton forces and dynamics in single-molecule systems such as DNA and molecular motors. In this work, we used optical tweezers to study the folding/unfolding dynamics of the APTSTX1-aptamer, a single-stranded DNA molecule with high affinity for saxitoxin (STX), a lethal neurotoxin. By measuring the transition force during (un)folding processes, we were able to characterize and distinguish the conformational changes of this aptamer in the presence of magnesium ions and toxin. This work was supported by molecular dynamics (MD) simulations to propose an unfolding mechanism of the aptamer-Mg+2 complex. Our results are a step towards the development of new aptamer-based STX sensors that are potentially cheaper and more sensitive than current alternatives.

The complementarity of object-relations and instinct theory.

Object-relations theory implicitly assumes primary drives to cope with the fact that some kinds of transaction with objects are not gratifying but are feared and avoided. Fairbairn's conception of motivation assumes that there is an independent primary drive which may be called 'need for love', independent of other gratifications. Such an instinctual-drive concept is defined solely by its direction towards a goal, and rests on an arbitrary intuition as to the 'real' goal of observed behaviour. As Freud pointed out, what is required for the objective identification of a drive is the discovery of its physiological source. Freud recognised that a drive can be gratified only by a 'specific action' performed upon a suitable object, and that object relations set up in very early life are especially long-lasting. The concept of fixation can bridge the gap between infantile instinctual reactions and adult object relations.

Problems in the concept of repression and proposals for their resolution.

The authors of this paper accept the reality of the phenomenon of repression and consider that it alone explains many kinds of psychopathology. Nevertheless, the assumption in Freud's sketch of the mechanism of repression that the ego continually guards against the repressed impulse becoming conscious creates a logical problem. That would require that the ego remain aware of the repressed. A mental act becomes conscious only by being made the object of a second mental act, not through possessing intrinsic consciousness. Some barrier must be set up to prevent this second mental act. Freud's concept of primal repression is compared with Kleinian concepts of splitting and projection, which seem to avoid some of his difficulties. It is proposed that as a result of initial outburst of anxiety, neurological blockages are set up between the neural registrations of certain images of instinctual gratification and those other neural organisations that could register the occurrence of those images. The latter thus remain unknown, though still affecting behaviour. Neurological findings suggest that some such mechanism is possible.

Suppression of spin-bath dynamics for improved coherence of multi-spin-qubit systems.

Multi-qubit systems are crucial for the advancement and application of quantum science. Such systems require maintaining long coherence times while increasing the number of qubits available for coherent manipulation. For solid-state spin systems, qubit coherence is closely related to fundamental questions of many-body spin dynamics. Here we apply a coherent spectroscopic technique to characterize the dynamics of the composite solid-state spin environment of nitrogen-vacancy colour centres in room temperature diamond. We identify a possible new mechanism in diamond for suppression of electronic spin-bath dynamics in the presence of a nuclear spin bath of sufficient concentration. This suppression enhances the efficacy of dynamical decoupling techniques, resulting in increased coherence times for multi-spin-qubit systems, thus paving the way for applications in quantum information, sensing and metrology.

Repetitive readout of a single electronic spin via quantum logic with nuclear spin ancillae.

Robust measurement of single quantum bits plays a key role in the realization of quantum computation and communication as well as in quantum metrology and sensing. We have implemented a method for the improved readout of single electronic spin qubits in solid-state systems. The method makes use of quantum logic operations on a system consisting of a single electronic spin and several proximal nuclear spin ancillae in order to repetitively readout the state of the electronic spin. Using coherent manipulation of a single nitrogen vacancy center in room-temperature diamond, full quantum control of an electronic-nuclear system consisting of up to three spins was achieved. We took advantage of a single nuclear-spin memory in order to obtain a 10-fold enhancement in the signal amplitude of the electronic spin readout. We also present a two-level, concatenated procedure to improve the readout by use of a pair of nuclear spin ancillae, an important step toward the realization of robust quantum information processors using electronic- and nuclear-spin qubits. Our technique can be used to improve the sensitivity and speed of spin-based nanoscale diamond magnetometers.