arXiv subjects

Jared H. Cole

Publications and source records attributed to Jared H. Cole.

At least 73 records · Page 4Linked to original sources

arXiv2015

All-optical thermometry and the thermal properties of the optically detected spin resonances of the NV center in nano-diamond

The negatively-charged nitrogen-vacancy (NV) center in diamond is at the frontier of quantum nano-metrology and bio-sensing. Recent attention has focused on the application of high-sensitivity thermometry using the spin resonances of NV centers in nano-diamond to sub-cellular biological and biomedical research. Here, we report a comprehensive investigation of the thermal properties of the center's spin resonances and demonstrate an alternate all-optical NV thermometry technique that exploits the temperature dependence of the center's optical Debye-Waller factor.

quant-ph↗

arXiv2015

Bloch-Redfield equations for modeling light-harvesting complexes

We challenge the misconception that Bloch-Redfield equations are a less powerful tool than phenomenological Lindblad equations for modeling exciton transport in photosynthetic complexes. This view predominantly originates from an indiscriminate use of the secular approximation. We provide a detailed description of how to model both coherent oscillations and several types of noise, giving explicit examples. All issues with non-positivity are overcome by a consistent straightforward physical noise model. Herein also lies the strength of the Bloch-Redfield approach because it facilitates the analysis of noise-effects by linking them back to physical parameters of the noise environment. This includes temporal and spatial correlations and the strength and type of interaction between the noise and the system of interest. Finally we analyze a prototypical dimer system as well as a 7-site Fenna-Matthews-Olson (FMO) complex in regards to spatial correlation length of the noise, noise strength, temperature and their connection to the transfer time and transfer.

physics.bio-ph↗

arXiv2014

Supersolid phases of light in extended Jaynes-Cummings-Hubbard systems

Jaynes-Cummings-Hubbard lattices provide unique properties for the study of correlated phases as they exhibit convenient state preparation and measurement, as well as "in situ" tuning of parameters. We show how to realize charge density and supersolid phases in Jaynes-Cummings-Hubbard lattices in the presence of long-range interactions. The long-range interactions are realized by the consideration of Rydberg states in coupled atom-cavity systems and the introduction of additional capacitive couplings in quantum-electrodynamics circuits. We demonstrate the emergence of supersolid and checkerboard solid phases, for calculations which take into account nearest neighbour couplings, through a mean-field decoupling.

cond-mat.other↗

arXiv2014

Correlated transport through junction arrays in the small Josephson energy limit: incoherent Cooper-pairs and hot electrons

We study correlated transport in a Josephson junction array for small Josephson energies. In this regime transport is dominated by Cooper-pair hopping, although we observe that quasiparticles can not be neglected. We assume that the energy dissipated by a Cooper-pair is absorbed by the intrinsic impedance of the array. This allows us to formulate explicit Cooper-pair hopping rates without adding any parameters to the system. We show that the current is correlated and crucially, these correlations rely fundamentally on the interplay between the Cooper-pairs and equilibrium quasiparticles.

cond-mat.mes-hall↗

arXiv2014

Atomic delocalisation as a microscopic origin of two-level defects in Josephson junctions

Identifying the microscopic origins of decoherence sources prevalent in Josephson junction based circuits is central to their use as functional quantum devices. Focussing on so called "strongly coupled" two-level defects, we construct a theoretical model using the atomic position of the oxygen which is spatially delocalised in the oxide forming the Josephson junction barrier. Using this model, we investigate which atomic configurations give rise to two-level behaviour of the type seen in experiments. We compute experimentally observable parameters for phase qubits and examine defect response under the effects of applied electric field and strain.

cond-mat.mes-hall↗

arXiv2014

Quantum metrology in the presence of spatially correlated noise: Restoring Heisenberg scaling

Environmental noise can hinder the metrological capabilities of entangled states. While the use of entanglement allows for Heisenberg-limited resolution, the largest permitted by quantum mechanics, deviations from strictly unitary dynamics quickly restore the standard scaling dictated by the central limit theorem. Product and maximally entangled states become asymptotically equivalent when the noisy evolution is both local and strictly Markovian. However, temporal correlations in the noise have been shown to lift this equivalence while fully (spatially) correlated noise allows for the identification of decoherence free subspaces. Here we analyze precision limits in the presence of noise with finite correlation length and show that there exist robust entangled state preparations which display persistent Heisenberg scaling despite the environmental decoherence, even for small correlation length. Our results emphasize the relevance of noise correlations in the study of quantum advantage and could be relevant beyond metrological applications.

quant-ph↗

arXiv2013

Correlated charge transport in bilinear tunnel junction arrays

We study theoretically the nature of correlations in space and time of the current in a one-dimensional bilinear array of tunnel junctions in the normal conduction limit, using the kinetic Monte Carlo (KMC) method. The bilinear array consists of two parallel rows of tunnel junctions, capacitively coupled in a ladder configuration. The electrostatic potential landscape and the charge-charge interaction length both depend on the circuit capacitances, which in turn influence transport and charge correlations in the array. We observe the formation of stationary charge states when only one rail is voltage biased. When a symmetric bias is applied to both rails, the site at which the positive and negative charge carriers recombine can drift throughout the array. We also calculate charge densities and auto- and cross-correlation functions.

cond-mat.mes-hall↗

arXiv2013

Stochastic Bloch-Redfield theory: quantum jumps in a solid-state environment

We discuss mapping the Bloch-Redfield master-equation to Lindblad form and then unravelling the resulting evolution into a stochastic Schrödinger equation according to the quantum-jump method. We give two approximations under which this mapping is valid. This approach enables us to study solid-state-systems of much larger sizes than is possible with the standard Bloch-Redfield master-equation, while still providing a systematic method for obtaining the jump operators and corresponding rates. We also show how the stochastic unravelling of the Bloch-Redfield equations becomes the kinetic Monte Carlo (KMC) algorithm in the secular approximation when the system-bath-coupling operators are given by tunnelling-operators between system-eigenstates. The stochastic unravelling is compared to the conventional Bloch-Redfield approach with the superconducting single electron transistor (SSET) as an example.

cond-mat.mes-hall↗

arXiv2013

Lasing and transport in a coupled quantum dot-resonator system

We investigate a double quantum dot coupled to a transmission line resonator. By driving a current through the double dot, a population inversion between the dot levels can be created, and a lasing state of the radiation field is generated within a sharp resonance window. The transport current correlates with the lasing state. The sharp resonance condition allows for resolving small differences in the dot properties. Dissipative processes in the quantum dots and their effect on the lasing and transport behavior are investigated.

cond-mat.mes-hall↗

arXiv2013

Analytic solutions to the central spin problem for Nitrogen Vacancy centres in diamond

Due to interest in both solid state based quantum computing architectures and the application of quantum mechanical systems to nanomagnetometry, there has been considerable recent attention focused on understanding the microscopic dynamics of solid state spin baths and their effects on the coherence of a controllable, coupled central electronic spin. Many analytic approaches are based on simplified phenomenological models in which it is difficult to capture much of the complex physics associated with this system. Conversely, numerical approaches reproduce this complex behaviour, but are limited in the amount of theoretical insight they can provide. Using a systematic approach based on the spatial statistics of spin bath constituents, we develop a purely analytic theory for the central spin decoherence problem of Nitrogen Vacancy centres in diamond that reproduces the experimental and numerical results found in the literature, whilst correcting a number of limitations and inaccuracies associated with existing analytical approaches.

cond-mat.mes-hall↗

arXiv2013

Electronic properties of delta-doped phosphorus layers in silicon and germanium

The Thomas-Fermi-Dirac (TFD) approximation and an sp3d5s* tight binding method were used to calculate the electronic properties of a delta-doped phosphorus layer in silicon. This self-consistent model improves on the computational efficiency of "more rigorous" empirical tight binding and ab initio density functional theory models without sacrificing the accuracy of these methods. The computational efficiency of the TFD model provides improved scalability for large multi-atom simulations, such as of nanoelectronic devices that have experimental interest. We also present the first theoretically calculated electronic properties of a delta-doped phosphorus layer in germanium as an application of this TFD model.

cond-mat.mes-hall↗

arXiv2013

Excitation- and state-transfer through spin chains in the presence of spatially correlated noise

We investigate the influence of environmental noise on spin networks and spin chains. In addition to the common model of an independent bath for each spin in the system we also consider noise with a finite spatial correlation length. We present the emergence of new dynamics and decoherence-free subspaces with increasing correlation length for both dephasing and dissipating environments. This leads to relaxation blocking of one spin by uncoupled surrounding spins. We then consider perfect state transfer through a spin chain in the presence of decoherence and discuss the dependence of the transfer quality on spatial noise correlation length. We identify qualitatively different features for dephasing and dissipative environments in spin-transfer problems.

quant-ph↗

arXiv2013

Derivation of Markovian master equations for spatially correlated decoherence

We introduce a general formalism to describe the effects of Markovian noise which is spatially correlated, typically decaying over some finite correlation length. For any system of interest, this formalism describes spatial correlations without the necessity to choose a particular microscopic model for the environment. We present a method of mapping the equations to Lindblad form and discuss functional forms for homogeneous spatial correlation functions. We also discuss two example microscopic models for the environment which exhibit non-trivial spatial-temporal correlation functions.

quant-ph↗

arXiv2012

Delocalised oxygen as the origin of two-level defects in Josephson junctions

One of the key problems facing superconducting qubits and other Josephson junction devices is the decohering effects of bi-stable material defects. Although a variety of phenomenological models exist, the true microscopic origin of these defects remains elusive. For the first time we show that these defects may arise from delocalisation of the atomic position of the oxygen in the oxide forming the Josephson junction barrier. Using a microscopic model, we compute experimentally observable parameters for phase qubits. Such defects are charge neutral but have non-zero response to both applied electric field and strain. This may explain the observed long coherence time of two-level defects in the presence of charge noise, while still coupling to the junction electric field and substrate phonons.

cond-mat.mes-hall↗

arXiv2012

Influence of two-level fluctuators on adiabatic passage techniques

We study the process of Stimulated Raman Adiabatic Passage (STIRAP) under the influence of a non-trivial solid-state environment, particularly the effect of two-level fluctuators (TLFs) as they are frequently present in solid-state devices. When the amplitudes of the driving-pulses used in STIRAP are in resonance with the level spacing of the fluctuators the quality of the protocol, i.e., the transferred population decreases sharply. In general the effect can not be reduced by speeding up the STIRAP process. We also discuss the effect of a structured noise environment on the process of Coherent Tunneling by Adiabatic Passage (CTAP). The effect of a weakly structured environment or TLFs with short coherence times on STIRAP and CTAP can be described by the Bloch-Redfield theory. For a strongly structured environment a higher-dimensional approach must be used, where the TLFs are treated as part of the system.

cond-mat.mes-hall↗

arXiv2012

Dual-probe decoherence microscopy: Probing pockets of coherence in a decohering environment

We study the use of a pair of qubits as a decoherence probe of a non-trivial environment. This dual-probe configuration is modelled by three two-level-systems which are coupled in a chain in which the middle system represents an environmental two-level-system (TLS). This TLS resides within the environment of the qubits and therefore its coupling to perturbing fluctuations (i.e. its decoherence) is assumed much stronger than the decoherence acting on the probe qubits. We study the evolution of such a tripartite system including the appearance of a decoherence-free state (dark state) and non-Markovian behaviour. We find that all parameters of this TLS can be obtained from measurements of one of the probe qubits. Furthermore we show the advantages of two qubits in probing environments and the new dynamics imposed by a TLS which couples to two qubits at once.

quant-ph↗

arXiv2011

Spin-guides and spin-splitters: Waveguide analogies in one-dimensional spin chains

Here we show a direct mapping between waveguide theory and spin chain transport, opening an alternative approach to quantum information transport in the solid-state. By applying temporally varying control profiles to a spin chain, we design a virtual waveguide or 'spin-guide' to conduct individual spin excitations along defined space-time trajectories of the chain. We explicitly show that the concepts of confinement, adiabatic bend loss and beamsplitting can be mapped from optical waveguide theory to spin-guides (and hence 'spin-splitters'). Importantly, the spatial scale of applied control pulses is required to be large compared to the inter-spin spacing, and thereby allowing the design of scalable control architectures.

quant-ph↗

arXiv2011

Correlation between lasing and transport properties in a quantum dot-resonator system

We study a double quantum dot system coherently coupled to an electromagnetic resonator. By suitably biasing the system, a population inversion can be created between the dot levels. The resulting lasing state exists within a narrow resonance window, where the transport current correlates with the lasing state. It allows probing the lasing state via a current measurement. Moreover, the resulting narrow current peak opens perspective for applications of the setup for high resolution measurements.

cond-mat.mes-hall↗