Questions tagged [quantum-mechanics]

Quantum mechanics describes the microscopic properties of nature in a regime where classical mechanics no longer applies. It explains phenomena such as the wave-particle duality, quantization of energy and the uncertainty principle and is generally used in single body systems. Use the quantum-field-theory tag for the theory of many-body quantum-mechanical systems.

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Difference between coherent and incoherent energy transfer (e.g. in photosynthesis)?

Several authors distinguish between incoherent and coherent when describing the energy transfer mechanism that forms the basis for photosynthesis. (e.g. Clegg & Sener 2010 and Keren & Paltiel ...
5answers
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What is temperature on a quantum level?

When I was in high school, I learned that temperature is kinetic energy. When I learned statistical physics, we learned that temperature is a statistical thing, and there was a formula for it. ...
0answers
21 views

Relative phase of a qubit

Is it possible to choose a suitable basis for a qubit so that the relative phase can be changed arbitrarily? In other words, do there exist rotation operators that can take a qubit with a specific ...
1answer
64 views

Finding the quadrature variance of a superposition of squeezed coherent states

How do you find the quadrature variance of a state $$\lvert x\rangle =\lvert a,b\rangle +\lvert a,-b\rangle$$ where $\lvert a,b\rangle = D(a) S(b) \lvert 0\rangle$? $\lvert x\rangle$ is a ...
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2answers
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Understanding wave function graph

I found this graph from the internet that interprets the graphical representation of wave function.I completely understand the wave function that is depicted by blue line but i really am confused ...
2answers
97 views

Interpretation of density matrix

In Landau’s Statistical Physics (part 1) , section 5, he writes:" In particular, it would be quite incorrect to suppose that the description by means of the density matrix signifies that the subsystem ...
1answer
67 views

Understanding the quantum mechanical state vector

According to Griffiths, there is a general state vector $|s(t)\rangle$ that encodes the state of the system. He also says that we take $\Psi(x, \ t) \ = \ \langle x | s(t) \rangle$. Would then mean ...
3answers
76 views

Is the concept of superpositions saying that the electron is actually in many states?

Basically when I read about it, yes. But I don't completely get why. Let me explain: If I throw a ball into a room and don't look, I would surely say that the ball is at one point in this room. Maybe ...
0answers
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Saturability problem about the quantum Cramer-Rao bound for the multi-parameter quantum metrology

I was studying the multi-parameter quantum metrology these days. And I was confused about the saturability of the quantum Cramer-Rao bound for the multiparameter problem. If all of the generators are ...
1answer
31 views

Effect of different reference frame on quantum entanglement measurement

According to what I read about entanglement, when you measure the spin of one of the entangled particles all the possibilities collapse to one value immediately and the other particle will give the ...
0answers
22 views

Non-Markovian noise coupled to atomic system

I want to calculate the density matrix element's average over all the realization of Gaussian colored noise when the atomic system is coupled to the said noise. I know how to do it for atomic energy ...
1answer
75 views

States for derivatives of wave function?

Given a wave function $\psi_t(x)$. The quantum state of a system at time t can be written as the sum of basis states multiplied by the amplitude: $$|t\rangle = \int \psi_t(x)|x\rangle dx^3$$ What ...
2answers
65 views

Do gravitational waves disperse/refract (like EM waves in a prism)?

I have read this question: What is the relationship between a gravitational wave and a graviton? where kingledion says: Gravitational waves were theorized a century ago and recently ...
1answer
32 views

Does this wave function from Zettili book (Quantum Mechanics) violate uncertainy principle?

I am not sure whether my question counts as homework and exercises or not, because I already know the answer. The problem is, I find Zettili answer rather unsatisfactory. Problem 1.11 (a) Find the ...
1answer
49 views

$s$-parameterized operator-valued Dirac delta function

So I am reading the book named 'Quantum Optics An Introduction' by Werner Vogel, Dirk-Gunnar Welsch, Sascha Wallentowitz and in the section 'Phase-space representations', I struggle to follow one step ...
3answers
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Can there be interference between a proton and an electron?

For example, we know that we can interfere two different electrons or two different protons by employing them in a double-slit experiment. Now suppose, we mix protons and electrons and shoot them ...
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2answers
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Is $[A,\exp{B}]=0 \Rightarrow [A,B]=0$ true?

The backward direction is trivial and this one probably too, but I just can't find a convincing argument. $A$, $B$ are Operators on a Hilbert Space (Ket Space).
2answers
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A doubt on waves

We know that every progressive wave depends on its position X and time variable T. y= Asin (kx- wt) My doubt is "Even an election is a wave (de broglie's hypothesis), but we cannot write its equation ...
1answer
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I am wondering if there is a way to calculate the amount of superposition that a quantum state is in. For example, if I have a $2$-qubit quantum system, with basis $\mathcal{B} = \{|00\rangle, |01\... 1answer 28 views Probability density of time-dependent wave functions Why is it so that probability density of eigenfunctions of time-dependent schrodinger equation are time independent while that of general wave functions (which are a combination of the eigenfunctions) ... 0answers 38 views Rigorous derivation of the ground state projector using euclidean time evolution Usually one argues that the euclidean path integral is able to recover the ground state of a system along the following lines: Take the time evolution operator$U(t,t_0)=e^{-iH(t-t_0)}$. Transform to ... 0answers 48 views How does$H^2$effect on the probability of photon detection? Lets consider an electromagnetic wave, between two ideal conductive plates. Maxwell's theory predicts appearance of a standing waves(of$\textbf{H}$and$\textbf{E}$), at that nodes($\textbf{E} = 0$)... 3answers 134 views Existence of Photon I was reading Feynman lectures on physics (volume 1) when I encountered the following paragraph: Returning again to quantum mechanics and fundamental physics, we cannot go into details of the ... 0answers 42 views Is it possible to know whether an arbitrary system is performing a quantum computation? Without knowing in advance that a physical system has been configured to do so, is it possible to determine whether that system is preforming, or has just performed a quantum computation? That is, if ... 1answer 55 views How is quantum physics translated into the world of electronics? [closed] I remember watching a documentary about early works in quantum physics and how it was essential to the microelectronics revolution and the invention of the transistor. What part exactly helped? Is ... 4answers 242 views Is it possible to see individual photons impressioning film? As part of a course in physics teaching, I am developing a small curriculum that will teach (the basics of) quantum mechanics to high school students. I need a simple way to show the quantization of ... 0answers 30 views Approximate solution to the resolvent of an open quantum system I have an open system which evolves according to some master equation: $$\partial_t\rho(t) = \mathcal{L}\rho(t)$$ where$\mathcal{L}$is the Liouvillian of the system which generates completely ... 3answers 90 views How does the photon energy formula$E=h\nu\$ mean the quantum nature of energy?

The frequency v can be less than 1. So the energy is starting from zero, and is continuous. The black body radiation is also continuous spectrum given an arbitrary temperature T.
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Can two particles be un-tangled without observing one or the other?

Is there a way to break the bond, sort to speak, without measuring or observing the particle? Or lets say we have 3 entangled particles A, B and C. Is there a way to untangle A and B without ...