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3
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0answers
101 views

Does quantum mechanics require classical measurement apparatus?

I am trying to learn quantum mechanics and I have a question. Landau, in his quantum mechanics book says that it is in principle impossible to formulate basic concepts of quantum mechanics without ...
3
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1answer
223 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 ...
13
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2answers
614 views

Are Thomas Breuer's subjective decoherence and Scott Aaronson's freebits with Knightian freedom the same things in essence?

In his remarkable works (1,2 and their recent development 3) Thomas Breuer proves by diagonalization the phenomenon that the observer cannot distinguish all phase space states of a system where he is ...
2
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4answers
245 views

What does quantum phenomena exist as prior to observation?

It's been said that according to the Schrodinger equation, independent of observation, particles exist in a state of a wave function, which is a series of potentialities rather than actual objects. ...
9
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3answers
337 views

Is the Copenhagen interpretation merely an approximation to quantum mechanics?

So, I'm reading Max Tegmark's Our Mathematical Universe (Knopf edition, p. 229). He's discussing Everett/MWI for a bit and I'm not really paying attention and then I wake up to this: [I]t's time ...
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4answers
605 views

Why doesn't a typical beam splitter cause a photon to decohere?

In many experiments in quantum mechanics, a single photon is sent to a mirror which it passes through or bounces off with 50% probability, then the same for some more similar mirrors, and at the end ...
3
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1answer
180 views

Quantum fluctuations in a classical domain?

"In the presence of chaos, even small fluctuations (including quantum fluctuations) can be amplified to produce large uncertainties in later behavior"(http://arxiv.org/pdf/gr-qc/9210010v2.pdf) Is there ...
14
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4answers
2k views

How is it possible that quantum phenomenons (e.g. superposition) are possible when all quantum particles are being constantly observed?

I don't understand how quantum mechanics (and therefore also quantum computers) can work given that while we work with quantum states, particles that this quantum state consist of cannot be observed, ...
4
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2answers
179 views

Without apparatus can we say that the system is measured(decohered) by the environment?

"Einselection" and "tridecompositional uniqueness theorem" seem to resolve the preferred basis problem. But the premise is that there are three parts in discussion.(system, apparatus, environment) ...
2
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0answers
134 views

How can the pre-measurement be fulfilled?

In the decoherence program, the pre-measurement refers to the evolution in which the system and apparatus form a Schmidt state. In Maximilian Schlosshauer's review article(2005), I read "the linearity ...
2
votes
2answers
158 views

What events lead to quantum decoherence?

Is there a very specific definition for all types of events where quantum decoherence occurs? Is it merely any event that is "thermodynamically irreversible" and/or "causes entropy to increase"? Is it ...
4
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4answers
1k views

Is the wave function of a particle re-created after a measurement stops?

Yeah, I haven't quite understood, or been told, what happens to, for example an electron and it's wavefunction, when you stop to measure it? I mean, an electron has a wave function describing it's ...
1
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0answers
60 views

What exactly constitutes a measurement? [duplicate]

As far as I understand it, quantum mechanics only predicts the probabilities of finding a system in some state of some observable when we make a measurement. So, what exactly constitutes a ...
10
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2answers
376 views

Are quantum decoherence and Everettian approaches to the measurement problem necessarily distinct?

As I understand it, there is a large contingent of physicists who believe that the measurement problem is "solved" by decoherence, without, for example, needing to postulate the existence of "many ...
2
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2answers
194 views

How does interaction of a system with the environment lead to the damping of interference terms?

A general way to describe a system $S$ that is entangled with an environment $E$ is $\rho_{S}=Tr(\rho_{SE})=\sum\limits_{m,n}c_mc^*_n |s_m\rangle \langle s_n| \langle e_n|e_m\rangle$ with ...
4
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1answer
126 views

Local decoherence and entropy

Consider a quantum system consisting of two subsystems, $A$ and $B$. Let $\rho$ be the density matrix of the whole system $A\cup B$. Let $|\alpha\rangle$, $\alpha = 1,2\cdots d_B$, be the states of ...
0
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2answers
216 views

The irreducible observer

This question probably verges on pseudo-science and probably sounds like gibberish, so please pardon me. But I'll ask it anyway. In an ideal lab experiment there is generally a separation between the ...
2
votes
1answer
655 views

What is the preferred basis objection to the many-worlds interpretation of quantum mechanics?

I've seen the preferred basis problem referred to in many places, but have not seen a clear explanation of what the problem is. For example, this question asks whether the problem has been solved, but ...
7
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1answer
221 views

Reason for decoherence time's dependence on variables?

Zurek 2001 is a review article on decoherence in quantum mechanics. Equation 5.36 on p. 24 gives an estimate of the decoherence time, which I'll paraphrase as follows: $ \frac{t_D}{t_R} = ...
6
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3answers
292 views

How can the quantum state of the universe decohere

Decoherence explains how a classical state appears once quantum information in a quantum state leaks out. But presumably that environment has its own quantum state which then leaks out to a larger ...
4
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1answer
496 views

If there is no collapse of the wave-function does this mean that the many worlds interpretation of QM must be wrong?

If as some people suggest, there is no collapse of the wave function (is there a standard name for this position), then must one rule out the many-worlds interpretation of QM?
6
votes
2answers
159 views

Can an observer be the observed?

As a supplement to this question as to whether particles can be observers, supposing that the answer is yes. One could suppose a setup where particle A is observing particle B, but what to stop us ...
10
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1answer
284 views

Can observers be particles?

Generally Quantum mechanics divides a system what is to be observed and an observer. This is generally taken to be some human being. But why restrict it to such? Why not a particle? Is there a good ...
1
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0answers
87 views

fast quantum random number generator + limited decoherence rate => Schrödinger cat state?

Suppose that fast quantum random number generator (QRNG, https://qrng.physik.hu-berlin.de/) is placed in a subsystem which has limited interaction with the rest of the world. What would happen if ...
12
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2answers
2k views

Is the preferred basis problem solved?

Once and for all: Is the preferred basis problem in the Everettian Interpretation of QM considered solved by decoherence or not? THere are a few people who claim that it's not, but it seems the vast ...
3
votes
1answer
634 views

The effect of Quantum Decoherence on density operators

Suppose we have a qubit in state $| \Psi \rangle = \alpha | 0 \rangle + \beta | 1 \rangle$ Suppose we expose this to decoherence, which we will express as the state $| R \rangle$ such that $$| 0 ...
0
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1answer
293 views

Books to study quantum thermodynamics and quantum decoherence [duplicate]

Possible Duplicate: Book recommendations My friend is having a hard time finding books to self-study quantum thermodynamics and quantum decoherence. (search on amaxon would bring almost no ...
3
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4answers
1k views

Decoherence and collapse

It is said that the decoherence does not solve the problem of measurement and/or the emergence of classicality, can somebody explain it with simple analogies or in a manner accessible to a ...
2
votes
1answer
813 views

What is quantum decoherence?

There is some part called quantum decoherence, and I am not sure why it is so sophisticated area. (according to the definition I see, what it seems to say is some probability turning into what we ...
5
votes
1answer
371 views

quantum field theoretic models of decoherence

I am interested in whether there is a field theoretic description (there is, so what is it?) of the tensor product (aka density matrix) model of open quantum systems. In particular, I am interested in ...
8
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4answers
2k views

Can the Montevideo interpretation of quantum mechanics do what it claims?

Partly inspired by the great responses to a my previous physics.SE question about "reversing gravitational decoherence, today I was rereading the intriguing papers by Gambini, Pullin, Porto, et al., ...
14
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8answers
3k views

Reversing gravitational decoherence

[Update: Thanks, everyone, for the wonderful replies! I learned something extremely interesting and relevant (namely, the basic way decoherence works in QFT), even though it wasn't what I thought I ...
3
votes
3answers
374 views

Quantum Decoherence and Macroscopic Phenomena

I don't really know what quantum decoherence is, but I have heard that it is used to explain why macroscopic objects do not seemingly follow quantum dynamics. Could someone please give a simple ...
2
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1answer
123 views

How are quantum phenomena in atoms and molecules protected against decoherence?

It became widely accepted that quantum effects don't show up in macroscopic objects due to the process of decoherence, in which the interaction with the enormous number of degrees of freedom of the ...
1
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1answer
54 views

In which way is decoherence not symmetric between the two considered systems?

If a quantum system interacts with a "big" quantum system, you have dephasing. The models of decoherence all have this atog aproach to them, about what is to understood of the interaction of the ...
1
vote
3answers
326 views

At what time exactly does decoherence happen? and retrodating

Take a qubit initialized to $|0\rangle$. Apply a Hadamard transform to it. Measure it with an apparatus along the $|0\rangle,\, |1\rangle$ basis. If zero, spare a living cat. If 1, kill the cat. ...
5
votes
4answers
482 views

Can a super-positioned human be used to differentiate between the Copenhagen interpretation and many-worlds?

I'm pretty new to quantum physics, so there's a good chance that I have this all backwards. However, by my understanding of the Copenhagen interpretation, the wave function 'collapses' upon ...
5
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2answers
1k views

Does the Hilbert space of the universe have to be infinite dimensional to make sense of quantum mechanics?

Does the Hilbert space of the universe have to be infinite dimensional to make sense of quantum mechanics? Otherwise, decoherence can never become exact. Does interpreting quantum mechanics require ...
5
votes
2answers
317 views

What is behind recoherence?

I am quite familiar with the concept of decoherence, and I heard that a system that has decohered could recohere after that, I was wondering what could cause the the coherences that have leaked into ...
8
votes
1answer
262 views

Any link between decoherence and renormalization?

I have been studying decoherence in quantum mechanics (not in qft, and don't know how it is described there) and renormalization in QFT and statistical field theory, I found at first a similarity ...
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3answers
1k views

Is the collapse of the wave function inherently time asymmetric?

Schroedinger's equation, as we all know, is time symmetric. In quantum field theory, we have to come up with a more sophisticated CPT reversal, but the essential point remains unchanged. However, the ...
5
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1answer
227 views

Do black holes play a role in quantum decoherence?

Sorry for such a vague question but I could have sworn I read somewhere that Hawking proposed the reason we might see a classically appearing universe is due to the possible role of black holes in ...
4
votes
3answers
312 views

Subjectivity of decoherence

I read that quantum decoherence is subjective, in the sense that two observers may not have the same "environment" and after each one has traced over those degrees of freedom they will end up with a ...
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3answers
1k views

Is decoherence even possible in anti de Sitter space?

Is decoherence even possible in anti de Sitter space? The spatial conformal boundary acts as a repulsive wall, thus turning anti de Sitter space into an eternally closed quantum system. Superpositions ...
2
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5answers
258 views

Open quantum systems and measuring devices

The Copenhagen interpretation by Niels Bohr insists that quantum systems do not exist independently of the measuring apparatus but only comes into being by the process of measurement itself. It is ...
4
votes
3answers
782 views

Does decoherence explain all instances of wave function collapse?

Specifically, how can decoherence explain the appearance of flecks of metallic silver on a photographic plate when exposed to the very weak light of a distant star? EDIT: Perhaps the advocates of ...
8
votes
3answers
2k views

A tutorial explanation of decoherence?

Is there a tutorial explanation as to how decoherence transforms a wavefunction (with a superposition of possible observable values) into a set of well-defined specific "classical" observable values ...