1
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1answer
39 views

Under what circumstances is observing a superposition possible?

According to Ian Stewart's 2013 Symmetry: A Very Short Introduction (pp. 119-120), Experiment and theory suggest that superposed states should not be observable as such; only individual ...
0
votes
1answer
46 views
4
votes
1answer
78 views

What exactly does Aaron D. O'Connell's experiment show?

I watched a TED talk by the scientist Aaron D. O'Connell about actually seeing quantum superposition. The link to the talk is :- ...
1
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1answer
115 views

Are we so sure about superposition?

Apparently particles can be anywhere when not observed. How strong is this theory really? Okay the wave-function can be collapsed through observation but how are we so sure that when an object is not ...
1
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1answer
70 views

When do we see particles to be in a superposition of energy states?

I have two doubts: Exactly when does this happen? and If we are in a superposition of states (lets say E1 and E2) and the particle absorbs a photon, what will happen? If E3-E1 = hf, will it go to E3? ...
3
votes
1answer
87 views

Schrödinger's cat and the difficulty of macroscopic superposition state

The Schrödinger's cat was regarded as peculiar since we seldom encounter a superposition state in macroscopic scale: $$ | \mathrm{dead \,\,cat} \rangle + | \mathrm{alive \,\, cat}\rangle $$ We more ...
0
votes
1answer
59 views

Can a particle in superposition act as x*(energy?)

I can't find an answer anywhere - I even asked my physics teacher, he hasn't a clue. Is superposition an illusion, or can a particle literally act as [x] particles?
3
votes
1answer
177 views

Bra-ket notation, Bits, & Superposition

I am a quantum computing enthusiast, and recently I stumbled upon this the following two propositions: $$ \alpha|1\rangle + \beta|0\rangle$$ What does this mean? My understanding of this is that: ...
0
votes
0answers
80 views

Superposition and density matrix. What are these states?

I just wanted to understand the following. Let's stay with the harmonic oscillator in QM, just to have an example at hand. First, there are all the different states for $n=1,2,...$. (Let's call them ...
1
vote
1answer
87 views

Linear Operators and their representations

I am currently learning Quantum mechanics on a slightly advanced level. I am curious in knowing if there are Linear Operators (Linear Maps) in the Hilbert Space (finite dimensional ones) that don't ...
0
votes
1answer
61 views

Quantum likelihood ratios?

Sorry if this is a dumb question, but I'm only starting to get to grips with this quantum malarkey. Anyway... Suppose I have two friends, Alice and Bob, both of whom have a random number generator. ...
0
votes
2answers
123 views

What's an atomic superstate/superposition, and how is it possible?

What's an atomic superstate/superposition, and how is it possible? I understand the basics - being something can be moving and staying still at the same time; the observer changes the behaviour - but ...
0
votes
0answers
53 views

Quantum eraser double slit experiment

In the quantum eraser double slit experiment, does the photon (or wavefunction) pass through one slit or both slits when different polarizers are placed over the slits?
0
votes
2answers
99 views

Basic Quantum Superposition

I'm looking to improve my understanding of quantum superposition. Consider the two-slit setup, where $|A\rangle$ is the state of the electron at the source, $|z\rangle$ is the state at some point on ...
1
vote
1answer
53 views

Spin half for the value of $|1 0\rangle$?

Spin-1/2 The eigenspinor , $X=aX_++bX_-$ $$X_+=\left( \begin{array}{cc} 1\\ 0\end{array} \right) $$$$X_-=\left( \begin{array}{cc} 0\\ 1\end{array} \right)$$ They are define like this because they ...
5
votes
6answers
948 views

How is quantum superposition different from mixed state?

According to Wikipedia, if a system has $50\%$ chance to be in state $\left|\psi_1\right>$ and $50\%$ to be in state $\left|\psi_2\right>$, then this is a mixed state. Now consider state ...
3
votes
1answer
96 views

Superpositions with two observers

This is a bit of an odd question. I'm not a physicist, so bear with me if I say something wrong. Lets say you have some sort of quantum event where matter is in a superposition. Standing next to you ...
0
votes
1answer
573 views

Expectation value of total energy for the quantum harmonic oscillator [closed]

A particles unnormalized wavefunction is given as $$\psi(x)=2\psi_1+\psi_2+2\psi_3.$$ How can I find $\langle E\rangle $ without calculating $\langle T\rangle$ or $\langle V\rangle $ ...
3
votes
2answers
262 views

Linearity of Quantum Mechanics?

The proof of the No-Cloning Theorem states "By the linearity of quantum mechanics, ..." -- Could someone please give me a rough sketch/outline of what this means. Does it have to do with the Hilbert ...
4
votes
1answer
1k views

Differences between pure/mixed/entangled/separable/superposed states

I am currently trying to establish a clear picture of pure/mixed/entangled/separable/superposed states. In the following I will always assume a basis of $|1\rangle$ and $|0\rangle$ for my quantum ...
-3
votes
1answer
88 views

Superposition and the Winning Jackpot Numbers

Let's say I buy myself a lottery ticket (Mega-Millions). I have $\frac{1}{175,711,536}$ chance of winning. Before I tune on the tv/radio and listen to the winning numbers (i.e. make an observation), ...
2
votes
1answer
338 views

How do we know superposition exists?

How do we know superposition exists? Has it been observed, or has it been deduced, and how certain are we? The Copenhagen Interpretation seems to imply that superposition collapses into one state ...
1
vote
1answer
246 views

Can we use intensities in the superposition principle?

In using the superposition principle to calculate intensities in interference patterns, can we add the intensities of the waves instead of their amplitudes? I think that amplitude account for the ...
3
votes
4answers
307 views

Is this statement about quantum mechanics valid?

In Philosophy of Language by William G. Lycan, there are the lines: Even apparent truths of logic, such as truths of the form "Either P or not P", might be abandoned in light of suitably weird ...
2
votes
2answers
201 views

What does the Copenhagen interpretation say about the position of a particle before measurement?

Suppose there is a particle in space. When we measure the position of that particle, we get a particular value with a probability that can be calculated from the wave function. But, according to the ...
0
votes
2answers
204 views

Is normalization consistent with Schrodinger's Equation?

Schrodinger's Equation does not set a limit on the size of wave functions but to normalize a wave function a limit must be set. How is this consistent physically and mathematically with Schrodinger's ...
1
vote
1answer
1k views

Deriving group velocity

At the introduction to quantum mechanic phase $v_p$ and group $v_g$ velocities are often presented. I know how to derive $v_p$ and get equation: $$ \scriptsize v_p=\frac{\omega}{k} $$ What i dont ...
2
votes
2answers
707 views

Is Schrödinger’s cat misleading? And what would happen if Planck constant is bigger?

Schrödinger’s cat, the thought experiment, makes it seem like as if measurement can cause a system to stop being in a superposition of states and become either one of the states (collapsed). So does ...
0
votes
4answers
498 views

Do multiple electrons exist during superposition?

Wikipedia says: Quantum superposition is a fundamental principle of quantum mechanics that holds that a physical system—such as an electron—exists partly in all its particular, theoretically ...
-3
votes
1answer
354 views

Quantum superposition and fate [closed]

First of all, sorry for my knowledge of physics. Maybe my question is too obvious but I want to ask it. I am thinking about fate and if it exist or no. According to my assumption if I take any ...
1
vote
2answers
161 views

According to wave function collapse you only have one outcome, so what happens to the other superpositions?

If the superpositions of a wave function are not needed because only one of the superpositions is allowed, what happens to the eigenvalues of the "null" superpositions? Is the energy transferred ...
2
votes
1answer
140 views

Can you tell if a particle is in superposition?

This may be an easy answer for anybody. Is it possible to detect if a particle A is still in a superposition via the sending a group of particles B through a box containing particle A?
8
votes
3answers
437 views

If superposition is possible in QM, why do we often assume systems are already in their eigenstates?

My understanding is that an arbitrary quantum-mechanical wavefunction can be written as a linear combination of eigenfunctions of some Hermitian operator, most commonly the Hamiltonian; when a ...
0
votes
4answers
822 views

What does superposition mean in quantum mechanics?

What does superposition mean in quantum mechanics? When I say $A+B=C$ (forces). I can mean push something with force $A$ + force $B$ together, and that is same as I push it with force $C$. But when ...
3
votes
3answers
274 views

How can we create superposition in QM?

How can we force a particle (let's say that we know this particle has spin up) to be in a superposition of spin up and down? Wouldn't literally any interaction of it with anything cause it to be in ...
2
votes
4answers
384 views

Does measuring destroy entanglement

Before measuring a quantum particle(photon) it exists in a superposition state, once we observe(measure) it, it settles in one of the possible states(destroying superposition). For entangled ...
2
votes
3answers
832 views

Classical vs qubits: Superposition

Since a quantum information lecture today I have been wondering what does it really mean for a state to be in superposition? Is this something that is answerable? This is what we learnt (or what I ...
9
votes
3answers
2k views

What's the difference between an entangled state, a superposed state and a cat state?

1) Can a state be entangled without also being a superposition? (Please give an example.) 2) Can a state be a superposition without being entangled? (Again, an example please.) 3) And what about ...
13
votes
4answers
907 views

Linearity of quantum mechanics and nonlinearity of macroscopic physics

We live in a world where almost all macroscopic physical phenomena are non-linear, while the description of microscopic phenomena is based on quantum mechanics which is linear by definition. What are ...