Search results for "Quantum physic"
showing 10 items of 1596 documents
Ultrafast Long-Distance Quantum Communication with Static Linear Optics
2015
We propose a projection measurement onto encoded Bell states with a static network of linear optical elements. By increasing the size of the quantum error correction code, both Bell measurement efficiency and photon-loss tolerance can be made arbitrarily high at the same time. As a main application, we show that all-optical quantum communication over large distances with communication rates similar to those of classical communication is possible solely based on local state teleportations using optical sources of encoded Bell states, fixed arrays of beam splitters, and photon detectors. As another application, generalizing state teleportation to gate teleportation for quantum computation, we…
Diagrammatic approach to quantum search
2014
We introduce a simple diagrammatic approach for estimating how a randomly walking quantum particle searches on a graph in continuous-time, which involves sketching small weighted graphs with self-loops and considering degenerate perturbation theory's effects on them. Using this method, we give the first example of degenerate perturbation theory solving search on a graph whose evolution occurs in a subspace whose dimension grows with $N$.
Relativistic quantum thermometry through a moving sensor
2023
Using a two-level moving probe, we address the temperature estimation of a static thermal bath modeled by a massless scalar field prepared in a thermal state. Different couplings of the probe to the field are discussed under various scenarios. We find that the thermometry is completely unaffected by the Lamb shift of the energy levels. We take into account the roles of probe velocity, its initial preparation, and environmental control parameters for achieving optimal temperature estimation. We show that a practical technique can be utilized to implement such a quantum thermometry. Finally, exploiting the thermal sensor moving at high velocity to probe temperature within a multiparameter-est…
Extracting work from random collisions: A model of a quantum heat engine
2022
We study the statistical distribution of the ergotropy and of the efficiency of a single-qubit battery ad of a single-qubit Otto engine, respectively fuelled by random collisions. The single qubit, our working fluid, is assumed to exchange energy with two reservoirs, a non-equilibrium "hot" reservoir and a zero temperature cold reservoir. The interactions between the qubit and the reservoirs is described in terms of a collision model of open system dynamics. The qubit interacts with the non-equilibrium reservoir (a large ensemble of qudits all prepared in the same pure state) via random unitary collisions and with the cold reservoir (a large ensemble of qubits in their ground state) via a p…
Design of a lambda configuration in artificial coherent nanostructures
2015
The implementation of a three-level Lambda System in artificial atoms would allow to perform advanced control tasks typical of quantum optics in the solid state realm, with photons in the $\mathrm{\mu m}$/mm range. However hardware constraints put an obstacle since protection from decoherence is often conflicting with efficient coupling to external fields. We address the problem of performing conventional STImulated Raman Adiabatic Passage (STIRAP) in the presence of low-frequency noise. We propose two strategies to defeat decoherence, based on "optimal symmetry breaking" and dynamical decoupling. We suggest how to apply to the different implementations of superconducting artificial atoms, …
Quantum phase transitions for an integrable quantum Rabi-like model with two interacting qubits
2022
A two-interacting-qubit quantum Rabi-like model with vanishing transverse fields on the qubit pair is studied. Independently of the coupling regime, this model can be exactly and unitarily reduced to two independent single-spin quantum Rabi models, where the spin-spin coupling plays the role of the transverse field. This transformation and the analytical treatment of the single-spin quantum Rabi model provide the key to prove the integrability of our model. The existence of different first-order quantum phase transitions, characterized by discontinuous two-spin magnetization, mean photon number, and concurrence, is brought to light.
Spin‐Chain‐Star Systems: Entangling Multiple Chains of Spin Qubits
2022
We consider spin-chain-star systems characterized by N-wise many-body interactions between the spins in each chain and the central one. We show that such systems can be exactly mapped into standard spin-star systems through unitary transformations. Such an approach allows the solution of the dynamic problem of an XX$X X$ spin-chain-star model and transparently shows the emergence of quantum correlations in the system, based on the idea of entanglement between chains.
Quantum Computation in a radio single mode cavity: the dissipative Jaynes and Cummings Model
2008
In this paper we have considered the interaction of a Jaynes and Cummings system with the electromagnetic field in its vacuum state and, solving the dynamical problem, we have analyzed the amount of entanglement induced in the bipartite system (atom + cavity mode) by the common electromagnetic reservoir. This has allowed us to quantitatively characterize the regime under which field-induced cooperative effects are not vanished by dissipation. Once the Decoherence Free Regime is reached, transient entanglement tends to become stationary and, therefore, usable for quantum gate implementation.
Spatial Search by Continuous-Time Quantum Walk with Multiple Marked Vertices
2015
In the typical spatial search problems solved by continuous-time quantum walk, changing the location of the marked vertices does not alter the search problem. In this paper, we consider search when this is no longer true. In particular, we analytically solve search on the "simplex of $K_M$ complete graphs" with all configurations of two marked vertices, two configurations of $M+1$ marked vertices, and two configurations of $2(M+1)$ marked vertices, showing that the location of the marked vertices can dramatically influence the required jumping rate of the quantum walk, such that using the wrong configuration's value can cause the search to fail. This sensitivity to the jumping rate is an is…
Classical nature of ordered phases: origin of spontaneous symmetry breaking
2014
We investigate the nature of spontaneous symmetry breaking in complex quantum systems by conjecturing that the maximally symmetry breaking quantum ground states are the most classical ones corresponding to an ordered phase. We make this argument quantitatively precise by showing that the ground states which realize the maximum breaking of the Hamiltonian symmetries are the only ones that: I) are always locally convertible, i.e. can be obtained from all other ground states by local operations and classical communication, while the reverse is never possible; II) minimize the monogamy inequality for bipartite entanglement; III) minimize quantum correlations, as measured by the quantum discord,…