NV Center Detection of Electric Fields and Low-Intensity Light (original) (raw)
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Dynamical control of electron spin coherence in a quantum dot: A theoretical study
Physical Review B, 2007
We investigate the performance of dynamical decoupling methods at suppressing electron spin decoherence from a low-temperature nuclear spin reservoir in a quantum dot. The controlled dynamics is studied through exact numerical simulation, with emphasis on realistic pulse delays and long-time limit. Our results show that optimal performance for this system is attained by a periodic protocol exploiting concatenated design, with control rates substantially slower than expected from the upper spectral cutoff of the bath. For a known initial electron spin state, coherence can saturate at long times, signaling the creation of a stable "spin-locked" decoherence-free subspace. Analytical insight on saturation is obtained for a simple echo protocol, in good agreement with numerical results.
Controlling the state of quantum spins with electric currents
Nature Physics, 2010
A current of spin-polarized electrons senses and controls the magnetic state of nanostructured materials 1 . Obtaining similar electrical access to quantum spin systems, such as singlemolecule magnets, is still in its infancy 2 . Recent progress has been achieved by probing the spin system near thermal equilibrium 3-9 . However, it is the elusive non-equilibrium properties of the excited states that govern the time evolution of such structures and will ultimately establish the feasibility of applications in data storage 2,10 and quantum information processing 11,12 . Here we use spin-polarized scanning tunnelling microscopy 13 to pump electron spins of atoms on surfaces into highly excited states and sense the resulting spatial orientation of the spin. This electrical control culminates in complete inversion of the spin-state population and gives experimental access to the spin relaxation times of each excited state. The direction of current flow determines the orientation of the atom's spin, indicating that electrical switching and sensing of future magnetic bits is feasible in the quantum regime.
APS, 2014
Within the framework of a general three-level problem, the dynamics of the nitrogen-vacancy (NV) spin is studied for the case of a special type of external driving consisting of a set of continuous fields with decreasing intensities. Such a set has been proposed for minimizing coherence losses. Each new driving field with smaller intensity is designed to protect against the fluctuations induced by the driving field at the preceding step with larger intensity. We show that indeed this particular type of external driving minimizes the loss of coherence, using purity and entropy as quantifiers for this purpose. As an illustration, we study the coherence loss of an NV spin due to a surrounding spin bath of 13 C nuclei.
Theory of the ground-state spin of the NV - center in diamond
Physical Review B - Condensed Matter and Materials Physics, 2012
The ground state spin of the negatively charged nitrogen-vacancy center in diamond has been the platform for the recent rapid expansion of new frontiers in quantum metrology and solid state quantum information processing. In ambient conditions, the spin has been demonstrated to be a high precision magnetic and electric field sensor as well as a solid state qubit capable of coupling with nearby nuclear and electronic spins. However, in spite of its many outstanding demonstrations, the theory of the spin has not yet been fully developed and there does not currently exist thorough explanations for many of its properties, such as the anisotropy of the electron g-factor and the existence of Stark effects and strain splittings. In this work, the theory of the ground state spin is fully developed for the first time using the molecular orbital theory of the center in order to provide detailed explanations for the spin's fine and hyperfine structures and its interactions with electric, magnetic and strain fields.
Solid-state electronic spin coherence time approaching one second
Nature Communications, 2013
Solid-state electronic spin systems such as nitrogen-vacancy (NV) color centers in diamond are promising for applications of quantum information, sensing, and metrology. However, a key challenge for such solid-state systems is to realize a spin coherence time that is much longer than the time for quantum spin manipulation protocols. Here we demonstrate an improvement of more than two orders of magnitude in the spin coherence time (T2) of NV centers compared to previous measurements: T2 ≈ 0.5 s at 77 K, which enables ∼ 10 7 coherent NV spin manipulations before decoherence. We employed dynamical decoupling pulse sequences to suppress NV spin decoherence due to magnetic noise, and found that T2 is limited to approximately half of the longitudinal spin relaxation time (T1) over a wide range of temperatures, which we attribute to phonon-induced decoherence. Our results apply to ensembles of NV spins and do not depend on the optimal choice of a specific NV, which could advance quantum sensing, enable squeezing and many-body entanglement in solid-state spin ensembles, and open a path to simulating a wide range of driven, interactiondominated quantum many-body Hamiltonians.
In many realizations of electron spin qubits the dominant source of decoherence is the fluctuating nuclear spin bath of the host material. The slowness of this bath lends itself to a promising mitigation strategy where the nuclear spin bath is prepared in a narrowed state with suppressed fluctuations. Here, this approach is realized for a two-electron spin qubit in a GaAs double quantum dot and a nearly ten-fold increase in the inhomogeneous dephasing time T * 2 is demonstrated. Between subsequent measurements, the bath is prepared by using the qubit as a feedback loop that first measures its nuclear environment by coherent precession, and then polarizes it depending on the final state. This procedure results in a stable fixed point at a nonzero polarization gradient between the two dots, which enables fast universal qubit control.
Physical Review Letters, 2010
In many realizations of electron spin qubits the dominant source of decoherence is the fluctuating nuclear spin bath of the host material. The slowness of this bath lends itself to a promising mitigation strategy where the nuclear spin bath is prepared in a narrowed state with suppressed fluctuations. Here, this approach is realized for a two-electron spin qubit in a GaAs double quantum dot and a nearly ten-fold increase in the inhomogeneous dephasing time T * 2 is demonstrated. Between subsequent measurements, the bath is prepared by using the qubit as a feedback loop that first measures its nuclear environment by coherent precession, and then polarizes it depending on the final state. This procedure results in a stable fixed point at a nonzero polarization gradient between the two dots, which enables fast universal qubit control.
ANU Open Research (Australian National University), 2011
The ground-state spin of the negatively charged nitrogen-vacancy center in diamond has been the platform for the recent rapid expansion of new frontiers in quantum metrology and solid-state quantum-information processing. However, in spite of its many outstanding demonstrations, the theory of the spin has not yet been fully developed, and there do not currently exist thorough explanations for many of its properties, such as the anisotropy of the electron g factor and the existence of Stark effects and strain splittings. In this work, the theory of the ground-state spin is fully developed using the molecular orbital theory of the center in order to provide detailed explanations for the spin's fine and hyperfine structures and its interactions with electric, magnetic, and strain fields. Given these explanations, a general solution is obtained for the spin in any given electric-magnetic-strain field configuration, and the effects of the fields on the spin's coherent evolution, relaxation, and inhomogeneous dephasing are examined. Thus, this work provides the essential theoretical tools for the precise control and modeling of this remarkable spin in its current and future applications.
Electrical Control of Spin Relaxation in a Quantum Dot
Physical Review Letters, 2008
We demonstrate electrical control of the spin relaxation time T1 between Zeeman split spin states of a single electron in a lateral quantum dot. We find that relaxation is mediated by the spinorbit interaction, and by manipulating the orbital states of the dot using gate voltages we vary the relaxation rate W ≡ T1 −1 by over an order of magnitude. The dependence of W on orbital confinement agrees with theoretical predictions and from these data we extract the spin-orbit length. We also measure the dependence of W on magnetic field and demonstrate that spin-orbit mediated coupling to phonons is the dominant relaxation mechanism down to 1 T, where T1 exceeds 1 s. PACS numbers: 73.63.Kv, 03.67.Lx, Achieving macroscopic control of quantum states has become an important part of developing systems for applications in quantum computing and spintronics . Control of the spin states of individual electrons confined in quantum dots is of particular interest . In a magnetic field B the spin states of the electron are split by the Zeeman energy ∆ = |g|µ B B, providing a two level quantum system that can be used as a qubit for quantum computing or as the basis of spin memory . Recent experiments have demonstrated the ability to manipulate [5, 6] and read-out [7, 8] the electron's spin. An important remaining challenge is to better understand and control the interactions between the electron's spin and its solid-state environment.
We propose an optical means to realize a spin hall effect (SHE) in neutral atomic system by coupling the internal spin states of atoms to radiation. The interaction between the external optical fields and the atoms creates effective magnetic fields that act in opposite directions on "electrically" neutral atoms with opposite spin polarizations. This effect leads to a Landau level structure for each spin orientation in direct analogy with the familiar SHE in semiconductors. The conservation and topological properties of the spin current, and the creation of a pure spin current are discussed. PACS numbers: 72.25.Fe, 32.80.Qk, 72.25.Hg, 03.75.Lm Information devices based on spin states of particles require a lot less power consumption than equivalent charge based devices . To implement practical spin-based logical operations, a basic underlying theory, i.e. spin hall effect (SHE) has been widely studied for the creation of spin currents in semiconductors . Nearly all current publications on SHE involve some form of spinorbit coupling, including the interaction between charged particles in semiconductors and external electric field. The physics of SHE in semiconductors is: in the presence of spin-orbit coupling, the applied electric field leads to a transverse motion (perpendicular to the electric field), with spin-up and spin-down carriers moving oppositely to each other, creating a transverse spin current. However, spin current can also be generated by interacting optical fields with charged particles in semiconductors , even in absence of spin-orbit coupling .