Identifying and decoupling many-body interactions in spin ensembles in diamond

Abstract

In this work, we simulate the dynamics of varying density quasi-2D spin-ensembles in solid state systems, focusing on the Nitrogen-Vacancy (NV) centers in diamond. We consider the effects of various control sequences on the averaged dynamics of large ensembles of spins, under a realistic "spin-bath" environment. We reveal that spin-locking is efficient for decoupling spins initialized along the driving axis, both from coherent dipolar interactions, and from the external spin-bath environment, when the driving is two orders of magnitude stronger than the relevant coupling energies. Since the application of standard pulsed dynamical decoupling (DD) sequences leads to strong decoupling from the environment, while other specialized pulse sequences can decouple coherent dipolar interactions, such sequences can be used to identify the dominant interaction type. Moreover, a proper combination of pulsed decoupling sequences could lead to the suppression of both interaction types, allowing additional spin manipulations. Finally, we consider the effect of finitewidth pulses on these control protocols, and identify improved decoupling efficiency with increased pulse duration, resulting from the interplay of dephasing and coherent dynamics.

Creation of long-lived states in interacting spins coupled to a thermal bath

“…As a method for enhancing lifetimes of spin-coherences, the emergence of long-lived spin-locked states have found widespread application in various fields, enabling one to investigate and measure slow dynamic processes which would otherwise be obscured by dipolar relaxation [4][5][6]. Spin-locking forms the basis of all cross-polarization (CP) class of experiments and also finds applications in many recent qubit manipulation, preservation and noise analysis protocols including polarization transfer experiments on nitrogen vacancy (NV) centers in diamond [7][8][9][10][11][12][13][14]. The existing models which attempt at providing a theoretical basis for the origin of these steady-states, mostly rely on the assumption of an effective spin-temperature in a tilted rotating-frame [1][2][3][15][16][17][18][19][20].…”

Hamiltonian engineering of general two-body spin-1/2 interactions

“…In particular, the Nitrogen-Vacancy (NV) centers in diamond, which offer optical initialization and readout capabilities, and can be treated to some extent as spin-1/2 qubits, are widely used for sensing [4][5][6][7][8][9][10] and quantum information processing [11][12][13][14]. Manipulating the dipolar interactions within an ensemble of such spins could pave the way towards novel studies of manybody dynamics [15][16][17], the creation of quantum simulators and sensors [18], and generation of non-classical spin states [17,19]. Recent studies of such Hamiltonian engineering, analyzing the effects of control pulses from the Clifford rotation group, resulted in a novel scheme of generating certain types of Hamiltonians [18].Here, we use group theory to go beyond previous work, introducing a more general platform of interaction manipulations, namely pulse sequences defined by an icosahedral symmetry.…”

“…2 (a)], which was designed in NMR to decouple spin-1/2 dipolar interaction, while flipping the Zeeman term along the three axes of the Bloch-sphere. Due to the inequivalency between the two-level manifold of NV centers and spin-1/2 systems, the dipolar terms are not decoupled completely, and the isotropic part H iso = a<b ω (ab) σ (a) · σ (b) 3 remains [17,23] [Fig. 2 (a)].…”

“…4(b)], excluding additional isotropic terms (see derivation in the supplemental material [21]). For a product state initialized along the x-y plane of the Bloch-sphere, general spin dynamics under this Hamiltonian can be written as a closed analytic expression [17], providing deep physical understanding of the system, as well as simulation capabilities of large ensembles.…”

“…Substituting the constant external field B z in Eq. (5) by spin dependent coefficients {δ (a) z } may shed led on the effects of spin disorder and many-body localization [23], and form buliding blocks for solid-states quantum simulators [17,19].…”