scholarly journals Impossibility of Distinguishing Two Preparations for a Pure State from No-signaling

Quanta ◽  
2020 ◽  
Vol 9 (1) ◽  
pp. 16-21
Author(s):  
Arun K. Pati
Keyword(s):  
Quantum Theory ◽  
Infinite Number ◽  
Mixed State ◽  
Physical System ◽  
Pure State ◽  
Entangled State ◽  
No Signaling

A pure state of a physical system can be prepared in an infinite number of ways. Quantum theory dictates that given a pure state of a physical system it is impossible to distinguish two preparation procedures. Here, we show that the impossibility of distinguishing two preparation procedures for the same pure state follows from the no-signaling principle. Extending this result for a pure bipartite entangled state entails that the impossibility of distinguishing two preparation procedures for a mixed state follows from the impossibility of distinguishing two preparations for a pure bipartite state.Quanta 2020; 9: 16–21.

Entanglement

2017 ◽  
Author(s):  
Richard Healey
Keyword(s):  
Quantum Theory ◽  
Quantum State ◽  
Physical Condition ◽  
Physical System ◽  
Polarization State ◽  
Quantum Systems ◽  
Ghz State ◽  
Mathematical Representation ◽  
Entangled State ◽  
Physical Relation

Often a pair of quantum systems may be represented mathematically (by a vector) in a way each system alone cannot: the mathematical representation of the pair is said to be non-separable: Schrödinger called this feature of quantum theory entanglement. It would reflect a physical relation between a pair of systems only if a system’s mathematical representation were to describe its physical condition. Einstein and colleagues used an entangled state to argue that its quantum state does not completely describe the physical condition of a system to which it is assigned. A single physical system may be assigned a non-separable quantum state, as may a large number of systems, including electrons, photons, and ions. The GHZ state is an example of an entangled polarization state that may be assigned to three photons.

scholarly journals Derivation of the robustness from the concurrence

2021 ◽  
pp. 2150166
Author(s):  
Yu. S. Krynytskyi ◽  
A. R. Kuzmak
Keyword(s):  
Mixed State ◽  
Pure State ◽  
Quantitative Measure ◽  
Exact Expression ◽  
Entangled State ◽  
Special Cases ◽  
Qubit States

Adding the maximally mixed state with some weight to the entanglement system leads to disentanglement of the latter. For each predefined entangled state there exists a minimal value of this weight for which the system loses its entanglement properties. These values were proposed to be used as a quantitative measure of entanglement called robustness [G. Vidal and R. Tarrach, Phys. Rev. A 59, 141 (1999)]. Using the concurrence, we propose the derivation of this measure for the system of two-qubit. Namely, for a two-qubit pure state, an exact expression of robustness is obtained. Finally, in the same way, the robustness of special cases of mixed two-qubit states is calculated.

Quantum discord and entanglement of two atoms in a micromaser-type system

2016 ◽  
Vol 30 (15) ◽  
pp. 1650190
Author(s):  
Xue-Qun Yan ◽  
Fu-Zhong Wang
Keyword(s):  
Time Evolution ◽  
Mixed State ◽  
Quantum Discord ◽  
Type System ◽  
Complete Loss ◽  
Entangled State ◽  
Fock State

The correlations dynamics of two atoms in the case of a micromaser-type system is investigated. We show that the entangled state can be created by initially maximally mixed state and there exist collapse and revival phenomena for the time evolutions of both entanglement and quantum discord under the system considered as the field is initially in the Fock state. Our results confirm that entanglement and quantum discord have similar behaviors in certain time ranges, such as their oscillations during the time evolution being almost in phase, but they also present significant differences, such as quantum discord being maintained even after the complete loss of entanglement. Furthermore, we exhibit clearly that the dynamics of quantum discord under the action of environment are intimately related to the generation and evolution of entanglement.

Probabilistic secret sharing through noise quantum channe

2012 ◽  
Vol 12 (3&4) ◽  
pp. 253-261
Author(s):  
Satyabrata Adhikari ◽  
Indranil Chakrabarty ◽  
Pankaj Agrawal
Keyword(s):  
Quantum Information ◽  
Secret Sharing ◽  
Mixed State ◽  
Pure State ◽  
Noisy Channel ◽  
Noisy Channels ◽  
Superdense Coding ◽  
Classical Information ◽  
Phase Damping ◽  
Realistic Situation

In a realistic situation, the secret sharing of classical or quantum information will involve the transmission of this information through noisy channels. We consider a three qubit pure state. This state becomes a mixed-state when the qubits are distributed over noisy channels. We focus on a specific noisy channel, the phase-damping channel. We propose a protocol for secret sharing of classical information with this and related noisy channels. This protocol can also be thought of as cooperative superdense coding. We also discuss other noisy channels to examine the possibility of secret sharing of classical information.

MIXED-STATE ENTANGLEMENT IN THE LIGHT OF PURE-STATE ENTANGLEMENT CONSTRAINED BY SUPERSELECTION RULES

2005 ◽  
Author(s):  
STEPHEN D. BARTLETT ◽  
HOWARD. M. WISEMAN ◽  
ROBERT W. SPEKKENS ◽  
ANDREW C. DOHERTY
Keyword(s):  
Mixed State ◽  
Pure State

scholarly journals Einstein-Podolsky-Rosen correlation seen from moving observers

2003 ◽  
Vol 3 (3) ◽  
pp. 224-228
Author(s):  
H. Terashima ◽  
M. Ueda
Keyword(s):  
Quantum Theory ◽  
Quantum Communication ◽  
Relativistic Quantum ◽  
Entangled State ◽  
Local Correlation ◽  
Relativistic Quantum Theory ◽  
Gedanken Experiment ◽  
Einstein Podolsky Rosen ◽  
Non Local ◽  
Epr Pair

Within the framework of relativistic quantum theory, we consider the Einstein-Podolsky-Rosen (EPR) gedanken-experiment in which measurements of the spin are performed by moving observers. We find that the perfect anti-correlation in the same direction between the EPR pair no longer holds in the observers' frame. This does not imply a breakdown of the non-local correlation. We explicitly show that the observers must measure the spin in appropriately chosen different directions in order to observe the perfect anti-correlation. This fact should be taken into account in utilizing the entangled state in quantum communication by moving observers.

scholarly journals Does Observation Create Reality?

2021 ◽  
Vol 19 (1) ◽  
pp. 11-15
Author(s):  
Daegene Song
Keyword(s):  
Energy Transfer ◽  
Quantum Theory ◽  
Quantum System ◽  
Quantum Entanglement ◽  
Physical System ◽  
Information Transfer ◽  
Thought Experiment ◽  
Particle Creation ◽  
Physical World ◽  
Quantum Vacuum

It has been suggested that the locality of information transfer in quantum entanglement indicates that reality is subjective, meaning that there is an innate inseparability between the physical system being observed and the conscious mind of the observer. This paper attempts to outline the relation between macroscopic and microscopic worlds in the measurement process in regards to whether observation creates reality. Indeed, the Maxwell's demon thought experiment suggests a correlation between a microscopic (quantum) system and a macroscopic (classical) apparatus, which leads to an energy transfer from the quantum vacuum to the physical world, similar to particle creation from a vacuum. This explanation shows that observation in quantum theory conserves, rather than creates, energy.

Quantum theory, the Church–Turing principle and the universal quantum computer

1985 ◽  
Vol 400 (1818) ◽  
pp. 97-117 ◽  
Keyword(s):  
Quantum Theory ◽  
Complexity Theory ◽  
Turing Machine ◽  
Physical System ◽  
Quantum Computer ◽  
Physical Principle ◽  
Universal Turing Machine ◽  
Universal Quantum ◽  
Computing Machines ◽  
The Church

It is argued that underlying the Church–Turing hypothesis there is an implicit physical assertion. Here, this assertion is presented explicitly as a physical principle: ‘every finitely realizible physical system can be perfectly simulated by a universal model computing machine operating by finite means’. Classical physics and the universal Turing machine, because the former is continuous and the latter discrete, do not obey the principle, at least in the strong form above. A class of model computing machines that is the quantum generalization of the class of Turing machines is described, and it is shown that quantum theory and the 'universal quantum computer’ are compatible with the principle. Computing machines resembling the universal quantum computer could, in principle, be built and would have many remarkable properties not reproducible by any Turing machine. These do not include the computation of non-recursive functions, but they do include ‘quantum parallelism’, a method by which certain probabilistic tasks can be performed faster by a universal quantum computer than by any classical restriction of it. The intuitive explanation of these properties places an intolerable strain on all interpretations of quantum theory other than Everett’s. Some of the numerous connections between the quantum theory of computation and the rest of physics are explored. Quantum complexity theory allows a physically more reasonable definition of the ‘complexity’ or ‘knowledge’ in a physical system than does classical complexity theory.

Periodic semi-classical vacuum, instantons and anomalies

2019 ◽  
pp. 319-334
Author(s):  
Jean Zinn-Justin
Keyword(s):  
Quantum Theory ◽  
Cp Violation ◽  
Band Structure ◽  
Quantum Chromodynamics ◽  
Infinite Number ◽  
Classical Solutions ◽  
Imaginary Time ◽  
Homotopy Classes ◽  
Classical Action ◽  
Topological Charges

Chapter 18 describes a few systems where the classical action has an infinite number of degenerate minima but, in the quantum theory, this degeneracy is lifted by barrier penetration effects. The simplest example is the cosine periodic potential and leads to the band structure. Technically, this corresponds to the existence of instantons, solutions to classical equations in imaginary time. In all examples, we show that the classical solutions are constrained by Bogomolnyi’s inequalities, which involve topological charges associated to a winding number and defining homotopy classes. In the case of quantum chromodynamics, this leads to the famous strong CP violation problem.

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