arXiv subjects

Jacob M. Taylor

Publications and source records attributed to Jacob M. Taylor.

89 records · Page 5Linked to original sources

arXiv2015

Framework for learning agents in quantum environments

In this paper we provide a broad framework for describing learning agents in general quantum environments. We analyze the types of classically specified environments which allow for quantum enhancements in learning, by contrasting environments to quantum oracles. We show that whether or not quantum improvements are at all possible depends on the internal structure of the quantum environment. If the environments are constructed and the internal structure is appropriately chosen, or if the agent has limited capacities to influence the internal states of the environment, we show that improvements in learning times are possible in a broad range of scenarios. Such scenarios we call luck-favoring settings. The case of constructed environments is particularly relevant for the class of model-based learning agents, where our results imply a near-generic improvement.

quant-ph↗

arXiv2015

Optomechanical reference accelerometer

We present an optomechanical accelerometer with high dynamic range, high bandwidth and read-out noise levels below 8 $μ$g/$\sqrt{\mathrm{Hz}}$. The straightforward assembly and low cost of our device make it a prime candidate for on-site reference calibrations and autonomous navigation. We present experimental data taken with a vacuum sealed, portable prototype and deduce the achieved bias stability and scale factor accuracy. Additionally, we present a comprehensive model of the device physics that we use to analyze the fundamental noise sources and accuracy limitations of such devices.

physics.optics↗

arXiv2014

Quantum Nonlinear Optics Near Optomechanical Instabilities

Optomechanical systems provide a unique platform for observing quantum behavior of macroscopic objects. However, efforts towards realizing nonlinear behavior at the single photon level have been inhibited by the small size of the radiation pressure interaction. Here we show that it is not necessary to reach the single-photon strong-coupling regime in order to realize significant optomechanical nonlinearities. Instead, nonlinearities at the few quanta level can be achieved, even with weak-coupling, in a two-mode optomechanical system driven near instability. In this limit, we establish a new figure of merit for realizing strong nonlinearity which scales with the single-photon optomechanical coupling and the sideband resolution of the mechanical mode with respect to the cavity linewidth. We find that current devices based on optomechanical crystals, thought to be in the weak-coupling regime, can still achieve strong quantum nonlinearity; enabling deterministic interactions between single photons.

quant-ph↗

arXiv2014

Environment-assisted quantum control of a solid-state spin via coherent dark states

Understanding the interplay between a quantum system and its environment lies at the heart of quantum science and its applications. To-date most efforts have focused on circumventing decoherence induced by the environment by either protecting the system from the associated noise or by manipulating the environment directly. Recently, parallel efforts using the environment as a resource have emerged, which could enable dissipation-driven quantum computation and coupling of distant quantum bits. Here, we realize the optical control of a semiconductor quantum-dot spin by relying on its interaction with an adiabatically evolving spin environment. The emergence of hyperfine-induced, quasi-static optical selection rules enables the optical generation of coherent spin dark states without an external magnetic field. We show that the phase and amplitude of the lasers implement multi-axis manipulation of the basis spanned by the dark and bright states, enabling control via projection into a spin-superposition state. Our approach can be extended, within the scope of quantum control and feedback, to other systems interacting with an adiabatically evolving environment.

quant-ph↗

arXiv2014

Scanning localized magnetic fields in a microfluidic device with a single nitrogen vacancy center

Nitrogen vacancy (NV) color centers in diamond have emerged as highly versatile optical emitters that exhibit room temperature spin properties. These characteristics make NV centers ideal for magnetometry, which plays an important role in chemical and biological sensing applications. The integration of NV magnetometers with microfluidic systems could enable the study of isolated chemical and biological samples in a fluid environment with high spatial resolution. Here we demonstrate a method to perform localized magnetometry with nanometer spatial precision using a single NV center in a microfluidic device. We manipulate a magnetic particle within a liquid environment using a combination of planar microfluidic flow control and vertical magnetic actuation to achieve 3-dimensional manipulation. A diamond nanocrystal containing a single NV center is deposited in the microfluidic channels and acts as a local magnetic field probe. We map out the magnetic field distribution of the magnetic particle by varying its position relative to the diamond nanocrystal and performing optically resolved electron spin resonance (ESR) measurements. We control the magnetic particle position with a 48 nm precision and attain a magnetic field sensitivity of 17.5 microTesla/Hz^1/2. These results open up the possibility for studying local magnetic properties of biological and chemical systems with high sensitivity in an integrated microfluidic platform.

quant-ph↗

arXiv2013

Engineering three-body interaction and Pfaffian states in circuit QED systems

We demonstrate a scheme to engineer the three-body interaction in circuit-QED systems by tuning a fluxonium qubit. Connecting such qubits in a square lattice and controlling the tunneling dynamics, in the form of a synthesized magnetic field, for the photon-like excitations of the system, allows the implementation of a parent Hamiltonian whose ground state is the Pfaffian wave function. Furthermore, we show that the addition of the next-nearest neighbor tunneling stabilizes the ground state, recovering the expected topological degeneracy even for small lattices. Finally, we discuss the implementation of these ideas with the current technology.

quant-ph↗

arXiv2013

Graphene on silicon nitride for optoelectromechanical micromembrane resonators

Due to their exceptional mechanical and optical properties, dielectric silicon nitride (SiN) micromembrane resonators have become the centerpiece of many optomechanical experiments. Efficient capacitive coupling of the membrane to an electrical system would facilitate exciting hybrid optoelectromechanical devices. However, capacitive coupling of such dielectric membranes is rather weak. Here we add a single layer of graphene on SiN micromembranes and compare electromechanical coupling and mechanical properties to bare dielectric membranes and to membranes metallized with an aluminium layer. The electrostatic coupling of graphene coated membranes is found to be equal to a perfectly conductive membrane. Our results show that a single layer of graphene substantially enhances the electromechanical capacitive coupling without significantly adding mass, decreasing the superior mechanical quality factor or affecting the optical properties of SiN micromembrane resonators.

cond-mat.mes-hall↗

arXiv2013

Non-equilibrium Fractional Quantum Hall state of light

We investigate the quantum dynamics of systems involving small numbers of strongly interacting photons. Specifically, we develop an efficient method to investigate such systems when they are externally driven with a coherent field. Furthermore, we show how to quantify the many-body quantum state of light via correlation functions. Finally, we apply this method to two strongly interacting cases: the Bose-Hubbard and fractional quantum Hall models, and discuss an implementation of these ideas in atom-photon system.

quant-ph↗

arXiv2013

Beating the standard quantum limit for force sensing with a coupled two-mode optomechanical system

Optomechanics allows the transduction of weak forces to optical fields, with many efforts approaching the standard quantum limit. We consider force-sensing using a mirror-in-the-middle setup and use two coupled cavity modes originated from normal mode splitting for separating pump and probe fields. We find that this two-mode model can be reduced to an effective single-mode model, if we drive the pump mode strongly and detect the signal from the weak probe mode. The optimal force detection sensitivity at zero frequency (DC) is calculated and we show that one can beat the standard quantum limit by driving the cavity close to instability. The best sensitivity achievable is limited by mechanical thermal noise and by optical losses. We also find that the bandwidth where optimal sensitivity is maintained is proportional to the cavity damping in the resolved sideband regime. Finally, the squeezing spectrum of the output signal is calculated, and it shows almost perfect squeezing at DC is possible by using a high quality factor and low thermal phonon-number mechanical oscillator.

quant-ph↗

arXiv2012

Algorithmic Cooling of a Quantum Simulator

Controlled quantum mechanical devices provide a means of simulating more complex quantum systems exponentially faster than classical computers. Such "quantum simulators" rely heavily upon being able to prepare the ground state of Hamiltonians, whose properties can be used to calculate correlation functions or even the solution to certain classical computations. While adiabatic preparation remains the primary means of producing such ground states, here we provide a different avenue of preparation: cooling to the ground state via simulated dissipation. This is in direct analogy to contemporary efforts to realize generalized forms of simulated annealing in quantum systems.

quant-ph↗

arXiv2010

Interferometry with Synthetic Gauge Fields

We propose a compact atom interferometry scheme for measuring weak, time-dependent accelerations. Our proposal uses an ensemble of dilute trapped bosons with two internal states that couple to a synthetic gauge field with opposite charges. The trapped gauge field couples spin to momentum to allow time dependent accelerations to be continuously imparted on the internal states. We generalize this system to reduce noise and estimate the sensitivity of such a system to be S~10^-7 m / s^2 / Hz^1/2.

quant-ph↗

arXiv2008

Quantum Repeater with Encoding

We propose a new approach to implement quantum repeaters for long distance quantum communication. Our protocol generates a backbone of encoded Bell pairs and uses the procedure of classical error correction during simultaneous entanglement connection. We illustrate that the repeater protocol with simple Calderbank-Shor-Steane (CSS) encoding can significantly extend the communication distance, while still maintaining a fast key generation rate.

quant-ph↗

arXiv2008

Coherence of an optically illuminated single nuclear spin qubit

We investigate the coherence properties of individual nuclear spin quantum bits in diamond [Dutt et al., Science, 316, 1312 (2007)] when a proximal electronic spin associated with a nitrogen-vacancy (NV) center is being interrogated by optical radiation. The resulting nuclear spin dynamics are governed by time-dependent hyperfine interaction associated with rapid electronic transitions, which can be described by a spin-fluctuator model. We show that due to a process analogous to motional averaging in nuclear magnetic resonance, the nuclear spin coherence can be preserved after a large number of optical excitation cycles. Our theoretical analysis is in good agreement with experimental results. It indicates a novel approach that could potentially isolate the nuclear spin system completely from the electronic environment.

quant-ph↗

arXiv2007

Distributed Quantum Computation Based-on Small Quantum Registers

We describe and analyze an efficient register-based hybrid quantum computation scheme. Our scheme is based on probabilistic, heralded optical connection among local five-qubit quantum registers. We assume high fidelity local unitary operations within each register, but the error probability for initialization, measurement, and entanglement generation can be very high (~5%). We demonstrate that with a reasonable time overhead our scheme can achieve deterministic non-local coupling gates between arbitrary two registers with very high fidelity, limited only by the imperfections from the local unitary operation. We estimate the clock cycle and the effective error probability for implementation of quantum registers with ion-traps or nitrogen-vacancy (NV) centers. Our new scheme capitalizes on a new efficient two-level pumping scheme that in principle can create Bell pairs with arbitrarily high fidelity. We introduce a Markov chain model to study the stochastic process of entanglement pumping and map it to a deterministic process. Finally we discuss requirements for achieving fault-tolerant operation with our register-based hybrid scheme, and also present an alternative approach to fault-tolerant preparation of GHZ states.

quant-ph↗

arXiv2007

Optimal approach to quantum communication using dynamic programming

Reliable preparation of entanglement between distant systems is an outstanding problem in quantum information science and quantum communication. In practice, this has to be accomplished via noisy channels (such as optical fibers) that generally result in exponential attenuation of quantum signals at large distances. A special class of quantum error correction protocols--quantum repeater protocols--can be used to overcome such losses. In this work, we introduce a method for systematically optimizing existing protocols and developing new, more efficient protocols. Our approach makes use of a dynamic programming-based searching algorithm, the complexity of which scales only polynomially with the communication distance, letting us efficiently determine near-optimal solutions. We find significant improvements in both the speed and the final state fidelity for preparing long distance entangled states.

quant-ph↗

arXiv2007

Spin-Photon Entangling Diode

We propose a semiconductor device that can electrically generate entangled electron spin-photon states, providing a building block for entanglement of distant spins. The device consists of a p-i-n diode structure that incorporates a coupled double quantum dot. We show that electronic control of the diode bias and local gating allow for the generation of single photons that are entangled with a robust quantum memory based on the electron spins. Practical performance of this approach to controlled spin-photon entanglement is analyzed.

cond-mat.mes-hall↗

arXiv2006

Quantum optical interface for gate-controlled spintronic devices

We describe an opto-electronic structure in which charge and spin degrees of freedom in electrical gate-defined quantum dots can be coherently coupled to light. This is achieved via electron-electron interaction or via electron tunneling into a proximal self-assembled quantum dot. We illustrate potential applications of this approach by considering several quantum control techniques, including optical read-out of gate-controlled semiconductor quantum bits and controlled generation of entangled photon-spin pairs.

cond-mat.mes-hall↗