Spin-oscillator System Research Articles

Squeezing-enhanced parameter estimation with a hybrid spin-oscillator interferometer

Inspired by the recent work [Nature (London) 521, 336 (2015)], we propose a scheme to suppress the backaction-induced dephasing of the spin state in a spin-oscillator system by squeezing the quantum fluctuation of the two-mode oscillator. We show specifically that squeezing either on a single mode individually or on both modes simultaneously could be used to effectively suppress spin dephasing. Therefore, with a spin-oscillator interferometer input by the spin-dependent squeezing cat state, the sensitivity of the rotational parameter estimation can be significantly enhanced. Given that various squeezings on the two-mode vibrations of the oscillator have been experimentally demonstrated, the proposal could provide a possibility to implement the sensitive parameter estimation, particularly in the ion-trap system.

Generalized spin kitten states in a strongly coupled spin-oscillator system

Utilizing an adiabatic approximation method, a bipartite qudit-oscillator Hamiltonian is studied for low-spin values in both strong and ultrastrong coupling regimes. The quasiprobability densities on the hybrid factorized phase space are introduced. Integrating over a sector of the composite phase space, the quasiprobability distributions of its complementary subsystem are recovered. In the strong coupling regime, the qudit entropy displays a pattern of quasiperiodic collapses and revivals, where the latter coincide with locally minimum entropy configurations. Starting with a bipartite factorizable initial state, we observe that almost pure spin kitten type states dynamically develop at near-null values of entropy. The Hilbert-Schmidt distance measure of these states puts them metrically far away from the initial state. Other localized spin states form at locally minimum but significantly large values of entropy. The evolution to the nonclassical transitory spin states is displayed via the diagonal spin ${\mathrm{P}}_{\mathcal{Q}}$ representation. As another manifestation of nonclassicality the emergence of the spin-squeezed states during the bipartite evolution is observed. In the ultrastrong coupling domain, a large number of interaction-dependent modes and their harmonics are generated. The consequent randomization of the phases eliminates the quasiperiodicity of the system which is now driven towards a stabilization of the entropy that also undergoes stochastic fluctuations around a suitably stabilized value. In both the strong and ultrastrong coupling realms, antibunching of the photoemission events is realized particularly for the small spin values.

Geometric quantization of almost toric manifolds

Kostant gave a model for the real geometric quantization associated to polarizations via the cohomology associated to the sheaf of flat sections of a pre-quantum line bundle. This model is well-adapted for real polarizations given by integrable systems and toric manifolds. In the latter case, the cohomology can be computed counting integral points inside the associated Delzant polytope. In this article we extend Kostant's geometric quantization to semitoric integrable systems and almost toric manifolds. In these cases the dimension of the acting torus is smaller than half of the dimension of the manifold. In particular, we compute the cohomology groups associated to the geometric quantization if the real polarization is the one associated to an integrable system with focus-focus type singularities in dimension four. As application we determine models for the geometric quantization of K3 surfaces, a spin-spin system, the spherical pendulum, and a spin-oscillator system under this scheme.

Spin-stress and spin-strain coupling in diamond-based hybrid spin oscillator systems

Hybrid quantum systems, which combine quantum-mechanical systems with macroscopic mechanical oscillators, have attracted increasing interest as they are well suited as high-performance sensors or transducers in quantum computers. A promising candidate is based on diamond cantilevers, whose motion is coupled to embedded Nitrogen-Vacancy (NV) centers through crystal deformation. Even though this type of coupling has been investigated intensively in the past, several inconsistencies exist in available literature, and no complete and consistent theoretical description has been given thus far. To clarify and resolve these issues, we here develop a complete and consistent formalism to describe the coupling between the NV spin degree of freedom and crystal deformation in terms of stress, defined in the crystal coordinate system XYZ, and strain, defined in the four individual NV reference frames. We find that the stress-based approach is straightforward, yields compact expressions for stress-induced level shifts and therefore constitutes the preferred approach to be used in future advances in the field. In contrast, the strain-based formalism is much more complicated and requires extra care when transforming into the employed NV reference frames. Furthermore, we illustrate how the developed formalism can be employed to extract values for the spin-stress and spin-strain coupling constants from data published by Teissier et al..

Strain sensitivity and symmetry of 2.65 eV color center in diamond nanoscale needles

Color centers in diamond have unique applications as nanoscale field sensors. In particular, in the case of strain field, they are key components for the realization of strain-coupled hybrid spin-oscillator systems. Here, we report on the strain sensitivity of the color center emitting at 2.65 eV in diamond nanoscale needles. By contactless piezo-spectroscopy, we compare the strain sensitivity of this center with that of the well-known neutral nitrogen-vacancy (NV0) center. We demonstrate that the 2.65 eV center has a higher strain sensitivity than the NV0 center and can be explored as a strain sensor and/or for strain-coupled systems. Moreover, we perform polarization-resolved photoluminescence spectroscopy under a high uniaxial tensile stress and the polar behavior reported for the 2.65 eV center points out to a defect symmetry which is different from that of the NV0 center.

Hybrid continuous dynamical decoupling: a photon-phonon doubly dressed spin

We study the parametric interaction between a single nitrogen-vacancy electronic spin and a diamond mechanical resonator in which the spin is embedded. Coupling between spin and oscillator is achieved by crystal strain, which is generated upon actuation of the oscillator and which parametrically modulates the spins’ energy splitting. Under coherent microwave driving of the spin, this parametric drive leads to a locking of the spin Rabi frequency to the oscillator mode in the megahertz range. Both the Rabi oscillation decay time and the inhomogeneous spin dephasing time increase by two orders of magnitude under this spin-locking condition. We present routes to prolong the dephasing times even further, potentially to the relaxation time limit. The remarkable coherence protection that our hybrid spin-oscillator system offers is reminiscent of recently proposed concatenated continuous dynamical decoupling schemes and results from our robust, drift-free strain-coupling mechanism and the narrow linewidth of the high-quality diamond mechanical oscillator employed. Our findings suggest feasible applications in quantum information processing and sensing.

Synchronizing the Dynamics of a Single Nitrogen Vacancy Spin Qubit on a Parametrically Coupled Radio-Frequency Field through Microwave Dressing

A hybrid spin-oscillator system in parametric interaction is experimentally emulated using a single nitrogen vacancy (NV) spin qubit immersed in a radio frequency (rf) field and probed with a quasiresonant microwave (MW) field. We report on the MW-mediated locking of the NV spin dynamics onto the rf field, appearing when the MW-driven Rabi precession frequency approaches the rf frequency and for sufficiently large rf amplitudes. These signatures are analogous to a phononic Mollow triplet in the MW rotating frame for the parametric interaction and promise to have impact in spin-dependent force detection strategies.

Measuring mechanical motion with a single spin

We study theoretically the measurement of a mechanical oscillator using a single two-level system as a detector. In a recent experiment, we used a single electronic spin associated with a nitrogen–vacancy center in diamond to probe the thermal motion of a magnetized cantilever at room temperature (Kolkowitz et al 2012 Science335 1603). Here, we present a detailed analysis of the sensitivity limits of this technique, as well as the possibility to measure the zero-point motion of the oscillator. Further, we discuss the issue of measurement backaction in sequential measurements and find that although backaction heating can occur, it does not prohibit the detection of zero-point motion. Throughout the paper, we focus on the experimental implementation of a nitrogen–vacancy center coupled to a magnetic cantilever; however, our results are applicable to a wide class of spin–oscillator systems. The implications for the preparation of nonclassical states of a mechanical oscillator are also discussed.

Spin-oscillator model for the unzipping of biomolecules by mechanical force

A spin-oscillator system models unzipping of biomolecules (such as DNA, RNA, or proteins) subject to an external force. The system comprises a macroscopic degree of freedom, represented by a one-dimensional oscillator, and internal degrees of freedom, represented by Glauber spins with nearest-neighbor interaction and a coupling constant proportional to the oscillator position. At a critical value F(c) of an applied external force F, the oscillator rest position (order parameter) changes abruptly and the system undergoes a first-order phase transition. When the external force is cycled at different rates, the extension given by the oscillator position exhibits a hysteresis cycle at high loading rates, whereas it moves reversibly over the equilibrium force-extension curve at very low loading rates. Under constant force, the logarithm of the residence time at the stable and metastable oscillator rest position is proportional to F-F(c) as in an Arrhenius law.

Experimental search for 129Xe atomic EDM with nuclear spin maser technique

The development of a nuclear spin oscillator system, namely a spin maser with an external feedback, for use in the search for 129Xe atomic EDM is presented. By introducing a new current source for the B0 field solenoid, drifts in the maser frequency were remarkably suppressed. This in turn clearly brought out the correlation between the maser frequency and the environmental field. Correcting for the effect of the environmental field, the frequency precision of 5 nHz in the measurement time of 45,000s was attained. Origins of the remaining drifts in the maser frequency are now under investigation.

Spin–oscillatory coupling effect in parabolic magnetic field

We consider eigenvalue problem of the coupled spin–oscillator system in the external parabolic magnetic field B =(B 0+G′x+G″x 2) z ̂ . In result we obtain the energy spectrum exhibiting highly non-standard structure, due to the second gradient term. For some values of the latter and oscillatory frequency there is large energy difference between some magnetic sublevels. The spectrum allows, in principle, to identify frequency of the oscillator via the spectrum of spin sublevels coming only from one oscillatory level.