Characterizing out-of-equilibrium many-body dynamics is a complex but crucial task for quantum applications and understanding fundamental phenomena. A central question is the role of localization in quenching thermalization in many-body systems and whether such localization survives in the presence of interactions. Probing this question in real systems necessitates the development of an experimentally measurable metric that can distinguish between different types of localization. While it is known that the localized phase of interacting systems [many-body localization (MBL)] exhibits a long-time logarithmic growth in entanglement entropy that distinguishes it from the noninteracting case of Anderson localization (AL), entanglement entropy is difficult to measure experimentally. Here, we present a novel correlation metric, capable of distinguishing MBL from AL in high-temperature spin systems. We demonstrate the use of this metric to detect localization in a natural solid-state spin system using nuclear magnetic resonance (NMR). We engineer the natural Hamiltonian to controllably introduce disorder and interactions, and observe the emergence of localization. In particular, while our correlation metric saturates for AL, it slowly keeps increasing for MBL, demonstrating analogous features to entanglement entropy, as we show in simulations. Our results show that our NMR techniques, akin to measuring out-of-time correlations, are well suited for studying localization in spin systems.

Transport of quantum information in linear spin chains has been the subject of much theoretical work. Experimental studies by NMR in solid state spin systems (a natural implementation of such models) is complicated since the dipolar Hamiltonian is not solely comprised of nearest-neighbor XY-Heisenberg couplings. We present here a similarity transformation between the XY Hamiltonian and the double-quantum Hamiltonian, an interaction which is achievable with the collective control provided by radio-frequency pulses. Not only can this second Hamiltonian simulate the information transport in a spin chain, but it also creates coherent states, whose intensities give an experimental signature of the transport. This scheme makes it possible to study experimentally the transport of polarization beyond exactly solvable models and explore the appearance of quantum coherence and interference effects.

We report record high 29Si spin polarization obtained using dynamic nuclear polarization in microcrystalline silicon powder. Unpaired electrons in this silicon powder are due to dangling bonds in the amorphous region of this intrinsically heterogeneous sample. 29Si nuclei in the amorphous region become polarized by forced electron-nuclear spin flips driven by off-resonant microwave radiation while nuclei in the crystalline region are polarized by spin diffusion across crystalline boundaries. Hyperpolarized silicon microparticles have long T1 relaxation times and could be used as tracers for magnetic resonance imaging.

We show that nuclear spin subsystems can be completely controlled via microwave irradiation of resolved anisotropic hyperfine interactions with a nearby electron spin. Such indirect addressing of the nuclear spins via coupling to an electron allows us to create nuclear spin gates whose operational time is significantly faster than conventional direct addressing methods. We experimentally demonstrate the feasibility of this method on a solid-state ensemble system consisting of one electron and one nuclear spin.Coherent control of quantum systems promises optimal computation [1], secure communication [2], and new insight into the fundamental physics of many-body problems [3]. Solid-state proposals [4,5,6,7,8] for such quantum information processors employ isolated spin degrees of freedom which provide Hilbert spaces with long coherence times. Here we show how to exploit a local, isolated electron spin to coherently control nuclear spins. Moreover, we suggest that this approach provides a fast and reliable means of controlling nuclear spins and enables the electron spins of such solid-state systems to be used for state preparation and readout [9] of nuclear spin states, and additionally as a spin actuator for mediating nuclear-nuclear spin gates.Model System. The spin Hamiltonian of a single local electron spin with angular momentum, S = 1 2 and N nuclear spins, each with angular momentum I k = 1 2 , in the presence of a magnetic field B is [10]:Here β e is the Bohr magneton, γ k n is the gyromagnetic ratio;Ŝ andÎ k are the spin-1 2 operators. The secondrank tensors g, A k , δ, and D kl represent the electron gfactor, the hyperfine interaction, the chemical shift, and the nuclear dipole-dipole interaction respectively.In the regime where the static magnetic field B = B 0ẑ provides a good quantization axis for the electron spin, the Hamiltonian can be simplified by dropping the nonsecular terms which corresponds to keeping only electron interactions involving S z . The quantization axis of any nuclear spin depends on the magnitudes of the hyperfine interaction and the main magnetic field, as well as their relative orientations. When these two fields are comparable in magnitude [37] H 0 can be approximated by: (2) with N=1. The electron spin state is in an eigenstate of purely the Zeeman interaction, while the nuclear spin state is not an eigenfunction of the Zeeman interaction alone due to the anisotropic hyperfine interaction. Because α0|β1 = 0 and α0|β0 = 0 the electron spin operator (Ŝx) has finite probabilities between all levels (dashed arrows). This allows for universal control of the entire spin system. The filled and unfilled circles represent the relative spin state populations of the ensemble at thermal equilibrium. In our experimental setup the energy differences are ω12/2π = 7.8 MHz, ω34/2π = 40 MHz, ω14/2π = 12.005 GHz, ω23/2π = 11.954GHzThe nuclear dipole-dipole interaction is neglected as it is typically 10 2 times weaker than the hyperfine terms.As described in Figure 1 (N=1), the nuclear spin is qu...

Magnetic resonance imaging of hyperpolarized nuclei provides high image contrast with little or no background signal. To date, in-vivo applications of pre-hyperpolarized materials have been limited by relatively short nuclear spin relaxation times. Here, we investigate silicon nanoparticles as a new type of hyperpolarized magnetic resonance imaging agent. Nuclear spin relaxation times for a variety of Si nanoparticles are found to be remarkably long, ranging from many minutes to hours at room temperature, allowing hyperpolarized nanoparticles to be transported, administered, and imaged on practical time scales. Additionally, we demonstrate that Si nanoparticles can be surface functionalized using techniques common to other biologically targeted nanoparticle systems. These results suggest that Si nanoparticles can be used as a targetable, hyperpolarized magnetic resonance imaging agent with a large range of potential applications.