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Every-day electromagnetic radiation, such as radio and TV waves, is also an example of near coherent states (macroscopic quantum coherence). That should "give one pause" regarding the conventional demarcation between quantum and classical. The coherence in superfluidity should not be attributed to any subset of helium atoms; it is a kind of ...
For bosons, a Bose–Einstein condensate is an example of a system exhibiting macroscopic quantum coherence through a multiple occupied single-particle state. The classical electromagnetic field exhibits macroscopic quantum coherence. The most obvious example is the carrier signal for radio and TV.
Typical T 2 coherence times for a charge qubit are on the order of 1–2 μs. [5] Recent work has shown T 2 times approaching 100 μs using a type of charge qubit known as a transmon inside a three-dimensional superconducting cavity. [6] [7] Understanding the limits of T 2 is an active area of research in the field of superconducting quantum ...
A pure quantum state is a state that can not be written as a probabilistic mixture, or convex combination, of other quantum states. [5] There are several equivalent characterizations of pure states in the language of density operators. [9]: 73 A density operator represents a pure state if and only if:
This is the approach on which quantum optics is based and it is only through this more general approach that quantum statistical coherence, lasers and condensates could be interpreted or discovered. Another more recent phenomenon discovered via this approach is the Bose–Einstein correlation between particles and antiparticles [citation needed].
In physics, atomic coherence is the induced coherence between levels of a multi-level atomic system and an electromagnetic field. The internal state of an atom is characterized by a superposition of excited states and their associated energy levels .
Quantum mechanics is a fundamental theory that describes the behavior of nature at and below the scale of atoms. [2]: 1.1 It is the foundation of all quantum physics, which includes quantum chemistry, quantum field theory, quantum technology, and quantum information science. Quantum mechanics can describe many systems that classical physics cannot.
Unlike measurement based feedback, where the quantum state is measured (causing it to collapse) and control is conditioned on the classical measurement outcome, coherent feedback maintains the full quantum state and implements deterministic, non-destructive operations on the state, using fully quantum devices. One example is a mirror ...