1,721,168 research outputs found
The European Quantum Technologies Flagship Program
No full textQuantum technologies, such as quantum communication, computation, simulation as well as sensors
and metrology, address and manipulate individual quantum states and make use of superposition and
entanglement. Both companies and governments have realised the high disruptive potential of this
technology. Consequently, the European Commission has announced an ambitious agship
programme to start in 2018. Here, we sum up the history leading to the quantum technologies agship
programme and outline its envisioned goals and structure. We also give an overview of the strategic
research agenda for quantum communication, which the agship will pursue during its 10-year
runtime
Testing temporal Bell inequalities through repeated measurements, in rf-SQUIDs
No full textTemporal Bell-like inequalities are derived taking into account the influence of the measurement apparatus on the observed magnetic flux in an rf-SQUID. Quantum measurement theory is shown to predict violations of these inequalities only when the flux states corresponding to opposite current senses are not distinguishable. Thus rf-SQUIDs cannot help to discriminate realism and quantum mechanics at the macroscopic level
OPTIMAL MEASUREMENTS OF MAGNETIC-FLUX IN SUPERCONDUCTING CIRCUITS AND MACROSCOPIC QUANTUM-MECHANICS
No full textA model of repeated quantum measurements of magnetic flux in superconducting circuits manifesting tunneling is discussed. The perturbation due to the previous measurements of magnetic flux is always present unless quantum nondemolition measurements are performed. By replacing the classical notion of noninvasivity with this condition, temporal Bell-like inequalities allow one to test the observability at the macroscopic level of the conflict between realism and quantum theory
Quantum nondemolition measurements on two-level atomic systems and temporal Bell inequalities
No full textThe evolution of a two-level system subjected to stimulated transitions which is undergoing a sequence of measurements of the level occupation probability is evaluated. Its time correlation function is compared to the one obtained through the pure Schrodinger evolution. Systems of this kind have been recently proposed for testing the quantum mechanical predictions against those of macrorealistic theories, by means of temporal Bell inequalities. The classical requirement of noninvasivity, needed to define correlation functions in the realistic case, finds a quantum counterpart in the quantum nondemolition condition. The consequences on the observability of quantum mechanically predicted violations to temporal Bell inequalities are drawn and compared to the already dealt case of the rf-SQUID dynamics
Tunneling in rf-SQUIDs and tests of quantum mechanics at the macroscopic level
No full textSuperconducting devices such as rf-SQUIDs have been proposed to test the validity of quantum mechanics by means of Bell-like inequalities involving different-time correlation probabilities for measurements of magnetic flux. We calculate the quantum mechanical violations to such temporal Bell inequalities taking into account the effect of the measurement process on the probability distribution for the outcomes. We define a general criterion quantifying the observability of the violations and show that it is not fulfilled for the various experimental configurations proposed so far
Continuous Quantum Gate Sets and Pulse-Class Meta-Optimization
Full text linkReduction of the circuit depth of quantum circuits is a crucial bottleneck to enabling quantum technology. This depth is inversely proportional to the number of available quantum gates that have been synthesized. Moreover, quantum gate-synthesis and control problems exhibit a vast range of external parameter dependencies, both physical and application specific. In this paper, we address the possibility of learning families of optimal-control pulses that depend adaptively on various parameters, in order to obtain a global optimal mapping from the space of potential parameter values to the control space and hence to produce continuous classes of gates. Our proposed method is tested on different experimentally relevant quantum gates and proves capable of producing high-fidelity pulses even in the presence of multiple variables or uncertain parameters with wide ranges
Fast quantum gate via Feshbach-Pauli blocking in a nanoplasmonic trap
No full textWe propose a simple idea for realizing a quantum gate with two fermions in a double well trap via external optical pulses without addressing the atoms individually. The key components of the scheme are Feshbach resonance and Pauli blocking, which decouple unwanted states from the dynamics. As a physical example we study atoms in the presence of a magnetic Feshbach resonance in a nanoplasmonic trap and discuss the constraints on the operation times for realistic parameters, reaching a fidelity above 99.9% within 42μs, much shorter than existing atomic gate schemes. © 2014 American Physical Society
Quantum computing implementations with neutral particles
No full textWe review quantum information processing with cold neutral particles, that is, atoms or polar molecules. First, we analyze the best suited degrees of freedom of these particles for storing quantum information, and then we discuss both singleand two-qubit gate implementations. We focus our discussion mainly on collisional quantum gates, which are best suited for atom-chip-like devices, as well as on gate proposals conceived for optical lattices. Additionally, we analyze schemes both for cold atoms confined in optical cavities and hybrid approaches to entanglement generation, and we show how optimal control theory might be a powerful tool to enhance the speed up of the gate operations as well as to achieve high fidelities required for fault tolerant quantum computation. © Springer Science+Business Media, LLC 2011
Optimal control technique for many-body quantum dynamics
No full textWe present an efficient strategy for controlling a vast range of nonintegrable quantum many-body one-dimensional systems that can be merged with state-of-the-art tensor network simulation methods such as the density matrix renormalization group. To demonstrate its potential, we employ it to solve a major issue in current optical-lattice physics with ultracold atoms: we show how to reduce by about 2 orders of magnitude the time needed to bring a superfluid gas into a Mott insulator state, while suppressing defects by more than 1 order of magnitude as compared to current experiments. Finally, we show that the optimal pulse is robust against atom number fluctuations. © 2011 American Physical Society
Optimal driving of Bose-Einstein condensates in optical cavities
No full textWe apply quantum optimal control to enhance the performance of the experimental setup of Ref. [1], speeding up the system dynamics at time scales of the order of the quantum speed limit. We perform a fast crossing of the quantum phase transition the system undergoes under realistic experimental conditions, and we present a new scaling-based strategy to compute optimal pulses for systems at the thermodynamical limit
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