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## New answers tagged terminology

3

You have pinpointed an important nuance of quantum information theory. A perfectly entangled state is, in some sense, like a single bit in a one time pad: just two copies of a shared random bit. In fact, the teleportation protocol is perfectly analogous — not the same, but certainly analogous — to transmitting a message securely using a one-time ...

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The name seems appropriate if consider that it probably comes from the case when the manifold is the cotangent bundle of a manifold. Then a point on $T^*M$ is a pair $(x,\alpha)$, where $x$ is a point on $M$ and $\alpha$ a one form. The definition of the tautological one form is: the value of the form at a point $(x,\alpha)$ on a tangent vector is obtained ...

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I) On a general symplectic manifold $({\cal M},\omega)$ (typically called phase space by physicists), one can locally choose a symplectic potential $\theta\in \Gamma(T^{*}{\cal M}|_{\cal U})$, which is a one-form such that $$\tag{1} \mathrm{d}\theta~=~\omega,$$ cf. Poincare Lemma. Here ${\cal U}\subseteq {\cal M}$ denotes a local neighborhood. Note ...

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It means that the metric and its inverse are well-defined everywhere in the space-time.

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For instance, a Lagrangian $L = \partial_i \phi \partial^i \phi + m^2\phi^2$ has the same equation of movement that the Lagrangian $L' = \partial_i \phi \partial^i \phi + m^2(F\phi - \frac{F^2}{2})$. The Euler-Lagrange equation for $L'$ simply give $\Box \phi +m^2F=0$ and $F = \phi$, so we have $\Box \phi +m^2\phi=0$, which are the Euler-Lagrange ...

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Let's say you have a catapult that can be turned into a trebuchet by attaching a sling to the end of the projecting rod. And let's say that it always launches the object with its projecting rod moving at some particular angular velocity instantaneously before it is stopped. Adding the sling has some benefits in terms of launching something at an enemy. The ...

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Both operate on the same principle: the velocity of a point on a rigid body undergoing rotation is proportional to its distance from the pivot. The sling is simply an ingenious way to extend the distance of the the projectile from the pivot without extending the rigid arm. As the trebuchet arm moves in an arc, the sling exerts a centripetal force on the ...

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A simple answer: motion is relative thus, there is always an implied reference. In other words, if you read or hear the phrase "X is stationary", you should immediately think "stationary with respect to what?". Most often, it is the case that an unqualified "stationary" means "at rest with respect to the measuring apparatus" or "with respect to the lab". ...

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This term is used all the time in introductory classical physics. In that context, stationary usually means not moving in the laboratory frame. Thus, a block sitting on a table not doing much would be referred to as being stationary. If one studies relative motion, then stationary could mean not moving in whatever frame you're discussing.

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This is a really good question, with a mind-bending answer. Check this out: (A) Pick a random electron at a random time. How long (on average) do I need to wait until the next time it collides? (B) Pick a random electron at a random time. How long (on average) has it been since the last time it collided? (C) Pick a random electron that just collided. How ...

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Before looking for the critical parameters, let's review how mushroom clouds work. A large amount of energy is released at the source of the explosion, effectively a point source for our discussions. That large energy release causes a blast wave that propagates outward and leaves behind a core of very hot, high density gas. If the blast wave was strong, the ...

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The no-go results from Algebraic and Constructive QFT you mention deal with related but slightly different matters. (Edit: the previous version of the following paragraph was slightly misleading - Haag's theorem is actually stronger than I stated before; see below for details) Haag's theorem (which actually slightly predates the inception of Algebraic ...

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an interesting question, no doubts. Indeed most of the time we rely on conservation of quantum numbers but there is an underlying structure to this. In principle changing a particle with an antiparticle amounts to a CP transformation. This is a symmetry for electromagnetic and (supposedly) strong interactions. Because of this, it doesn't really matter what ...

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It started with conservation of quantum numbers, from baryon number when we did not know about quarks, to lepton number, when we discovered the positron.For the neutrino momentum and energy conservation played a role too, since it is only seen as a missing mass. In time the symmetries in the assignments of the quantum numbers became more and more evident ...

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Batteries produce a charge difference across the terminals as a result of a chemical reaction. A chemical gets changed into another one. Even in a rechargeable battery a chemical change takes place that is reversed. An electrolytic capacitor uses chemistry to create a thin layer with an electric field across it. The thinner layer than a "regular" capacitor ...

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Yes, for example, an object with a constant applied force and an oppositely directed speed dependent force has a terminal speed. The sum of forces is: $F_{NET} = F_A - kv$ Clearly, when the speed is large enough that $kv = F_A$, the net force is zero and the object stops accelerating - the object has reached terminal speed. See this hyperphysics article: ...

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The ground which locates in the non-inverting terminal of an Op-Amp is called virtual ground.

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I'll talk about the Ramsey method of oscillatory field, which is a method for detecting the resonance frequency of a system. Probably this is what you mean. Imagine you have a spin-1/2 particles ensemble (for simplicity, higher spins act in the same way under the first multipole approximation), and this spin is polarized along the z-direction. If you apply ...

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Fermi energy is difference of energies of highest and lowest occupied single state particle. But, Fermi level is the sum of total energy of a particle (i.e) the sum of kinetic and potential energies.

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Simply stated, in the area of contact dynamics, a unilateral (bilateral) constraint refers to a one-sided (two-sided) constraint, i.e. a constraint described$^1$ via an inequality (equality) of some constraint function $f(q,\dot{q},t)$, respectively. Here we are assuming that the variables $q^i$ are real (as opposed to complex). Technically, one demands ...

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I recently updated the wikipedia article on statistical ensembles which might be relevant. Basically, in classical physics the probability distribution for the state of a system is written as an integral over position and momentum as in your equation. It turns out to be necessary to choose an arbitrary unit of action (energy times time) in order to define ...

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A process where the energy is kept constant is called isoenergetic (or, if you prefer, iso-energetic). It also seems from the literature that a flow where the energy is constant when following a fluid particle is usually called an isoenergetic flow. Similarly, when the enthalpy is kept constant, the process (or the flow) is said to be isenthalpic (or ...

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