Soonwon Choi

Nuclear magnetic resonance detection and spectroscopy of single proteins using quantum logic

Sensing single proteins with diamonds Nuclear magnetic resonance is a powerful technique for medical imaging and the structural analysis of materials, but is usually associated with large-volume samples. Lovchinsky et al. exploited the magnetic properties of a single spin associated with a defect in diamond and manipulated it with a quantum-logic protocol. They demonstrated the magnetic resonance detection and spectroscopy of multiple nuclear species within individual ubiquitin proteins attached to a specially treated diamond surface at room temperature. Science, this issue p. 836 The quantum properties of diamond are used for magnetic resonance spectroscopy of single proteins. Nuclear magnetic resonance spectroscopy is a powerful tool for the structural analysis of organic compounds and biomolecules but typically requires macroscopic sample quantities. We use a sensor, which consists of two quantum bits corresponding to an electronic spin and an ancillary nuclear spin, to demonstrate room temperature magnetic resonance detection and spectroscopy of multiple nuclear species within individual ubiquitin proteins attached to the diamond surface. Using quantum logic to improve readout fidelity and a surface-treatment technique to extend the spin coherence time of shallow nitrogen-vacancy centers, we demonstrate magnetic field sensitivity sufficient to detect individual proton spins within 1 second of integration. This gain in sensitivity enables high-confidence detection of individual proteins and allows us to observe spectral features that reveal information about their chemical composition.

Observation of discrete time-crystalline order in a disordered dipolar many-body system

Understanding quantum dynamics away from equilibrium is an outstanding challenge in the modern physical sciences. Out-of-equilibrium systems can display a rich variety of phenomena, including self-organized synchronization and dynamical phase transitions. More recently, advances in the controlled manipulation of isolated many-body systems have enabled detailed studies of non-equilibrium phases in strongly interacting quantum matter; for example, the interplay between periodic driving, disorder and strong interactions has been predicted to result in exotic ‘time-crystalline’ phases, in which a system exhibits temporal correlations at integer multiples of the fundamental driving period, breaking the discrete time-translational symmetry of the underlying drive. Here we report the experimental observation of such discrete time-crystalline order in a driven, disordered ensemble of about one million dipolar spin impurities in diamond at room temperature. We observe long-lived temporal correlations, experimentally identify the phase boundary and find that the temporal order is protected by strong interactions. This order is remarkably stable to perturbations, even in the presence of slow thermalization. Our work opens the door to exploring dynamical phases of matter and controlling interacting, disordered many-body systems.

Probing Johnson noise and ballistic transport in normal metals with a single-spin qubit

Listen to the quantum art of noise Electrons in metals are subject to thermally induced noise that can generate tiny magnetic fields. For quantum electronic applications, the noise and magnetic fields can be damaging. Kolkowitz et al. show that the spin properties of single defects in diamond can be used to probe the noise. The findings provide insight into how the noise is generated, which could help to mitigate its damaging effects in sensitive quantum electronic circuits. Science, this issue p. 1129 Single spin defects in diamond can be used to probe electronic noise in thin metal films. [Also see Perspective by McGuinness and Jelezko] Thermally induced electrical currents, known as Johnson noise, cause fluctuating electric and magnetic fields in proximity to a conductor. These fluctuations are intrinsically related to the conductivity of the metal. We use single-spin qubits associated with nitrogen-vacancy centers in diamond to probe Johnson noise in the vicinity of conductive silver films. Measurements of polycrystalline silver films over a range of distances (20 to 200 nanometers) and temperatures (10 to 300 kelvin) are consistent with the classically expected behavior of the magnetic fluctuations. However, we find that Johnson noise is markedly suppressed next to single-crystal films, indicative of a substantial deviation from Ohm’s law at length scales below the electron mean free path. Our results are consistent with a generalized model that accounts for the ballistic motion of electrons in the metal, indicating that under the appropriate conditions, nearby electrodes may be used for controlling nanoscale optoelectronic, atomic, and solid-state quantum systems.

Magnetic resonance spectroscopy of an atomically thin material using a single-spin qubit

Getting a sense of atomically thin materials Two-dimensional materials such as graphene and transition metal dichalcogenides provide a powerful platform for optoelectronic applications. As the materials get thinner, however, characterizing the electronic properties can present an experimental challenge. Lovchinsky et al. demonstrate that atomic-like impurities in diamond can be used to probe the properties of 2D materials by nanometer-scale nuclear quadrupole resonance spectroscopy. Coherent manipulation of shallow nitrogen-vacancy color centers enabled probing of nanoscale ensembles down to several tens of nuclear spins in atomically thin hexagonal boron nitride. Science, this issue p. 503 A nitrogen-vacancy center in diamond is used to probe the electronic properties of atomically thin materials. Two-dimensional (2D) materials offer a promising platform for exploring condensed matter phenomena and developing technological applications. However, the reduction of material dimensions to the atomic scale poses a challenge for traditional measurement and interfacing techniques that typically couple to macroscopic observables. We demonstrate a method for probing the properties of 2D materials via nanometer-scale nuclear quadrupole resonance (NQR) spectroscopy using individual atomlike impurities in diamond. Coherent manipulation of shallow nitrogen-vacancy (NV) color centers enables the probing of nanoscale ensembles down to approximately 30 nuclear spins in atomically thin hexagonal boron nitride (h-BN). The characterization of low-dimensional nanoscale materials could enable the development of new quantum hybrid systems, combining atomlike systems coherently coupled with individual atoms in 2D materials.

Scattering resonances and bound states for strongly interacting Rydberg polaritons

We provide a theoretical framework describing slow-light polaritons interacting via atomic Rydberg states. We use a diagrammatic method to analytically derive the scattering properties of two polaritons. We identify parameter regimes where polariton-polariton interactions are repulsive. Furthermore, in the regime of attractive interactions, we identify multiple two-polariton bound states, calculate their dispersion, and study the resulting scattering resonances. Finally, the two-particle scattering properties allow us to derive the effective low-energy many-body Hamiltonian. This theoretical platform is applicable to ongoing experiments.

Depolarization Dynamics in a Strongly Interacting Solid-State Spin Ensemble

We study the depolarization dynamics of a dense ensemble of dipolar interacting spins, associated with nitrogen-vacancy centers in diamond. We observe anomalously fast, density-dependent, and nonexponential spin relaxation. To explain these observations, we propose a microscopic model where an interplay of long-range interactions, disorder, and dissipation leads to predictions that are in quantitative agreement with both current and prior experimental results. Our results pave the way for controlled many-body experiments with long-lived and strongly interacting ensembles of solid-state spins.

Symmetry-protected collisions between strongly interacting photons.

Realizing robust quantum phenomena in strongly interacting systems is one of the central challenges in modern physical science. Approaches ranging from topological protection to quantum error correction are currently being explored across many different experimental platforms, including electrons in condensed-matter systems, trapped atoms and photons. Although photon–photon interactions are typically negligible in conventional optical media, strong interactions between individual photons have recently been engineered in several systems. Here, using coherent coupling between light and Rydberg excitations in an ultracold atomic gas, we demonstrate a controlled and coherent exchange collision between two photons that is accompanied by a π/2 phase shift. The effect is robust in that the value of the phase shift is determined by the interaction symmetry rather than the precise experimental parameters, and in that it occurs under conditions where photon absorption is minimal. The measured phase shift of 0.48(3)π is in excellent agreement with a theoretical model. These observations open a route to realizing robust single-photon switches and all-optical quantum logic gates, and to exploring novel quantum many-body phenomena with strongly interacting photons.

Universal photonic quantum computation via time-delayed feedback

Significance Creating large entangled states with photons as quantum information carriers is a central challenge for quantum information processing. Since photons do not interact directly, entangling them requires a nonlinear element. One approach is to sequentially generate photons using a quantum emitter that can induce quantum correlations between photons. Here we show that delayed quantum feedback dramatically expands the class of achievable photonic quantum states. In particular, we show that in state-of-the-art experiments with single atom-like quantum emitters, the most basic form of delayed quantum feedback already allows for creation of states that are universal resources for quantum computation. This opens avenues for quantum information processing with photons using minimal experimental resources. We propose and analyze a deterministic protocol to generate two-dimensional photonic cluster states using a single quantum emitter via time-delayed quantum feedback. As a physical implementation, we consider a single atom or atom-like system coupled to a 1D waveguide with a distant mirror, where guided photons represent the qubits, while the mirror allows the implementation of feedback. We identify the class of many-body quantum states that can be produced using this approach and characterize them in terms of 2D tensor network states.Hannes Pichler, 2, ∗ Soonwon Choi, ∗ Peter Zoller, 4 and Mikhail D. Lukin ITAMP, Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138, USA Physics Department, Harvard University, Cambridge, Massachusetts 02138, USA Institute for Theoretical Physics, University of Innsbruck, A-6020 Innsbruck, Austria Institute for Quantum Optics and Quantum Information of the Austrian Academy of Sciences, A-6020 Innsbruck, Austria (Dated: February 8, 2017)

Dynamics of quantum information in many-body localized systems

We characterize the information dynamics of strongly disordered systems using a combination of analytics, exact diagonalization, and matrix product operator simulations. More specifically, we study the spreading of quantum information in three different scenarios: thermalizing, Anderson localized, and many-body localized. We qualitatively distinguish these cases by quantifying the amount of remnant information in a local region. The nature of the dynamics is further explored by computing the propagation of mutual information with respect to varying partitions. Finally, we demonstrate that classical simulability, as captured by the magnitude of MPO truncation errors, exhibits enhanced fluctuations near the localization transition, suggesting the possibility of its use as a diagnostic of the critical point.