Decoherence Definition and 177 Threads

Is it possible, and fruitful, to use certain conceptual and technical tools from effective field theory (coarse-graining/integrating-out, power-counting, matching, RG) to think about the relationship between the fundamental (quantum) and the emergent (classical), both to account for the...

According to recent podcast between Jacob Barandes and Sean Carroll, Barandes claims that putting a sensitive qubit near one of the slits of a double slit interference experiment is sufficient to break the interference pattern. Here are his words from the official transcript: Is that true...

Suppose we have a quantum system ##S##, an apparatus ##A##, and an observer, say Alice, ##O##. WLOG let ##S## be a spin-##1/2##particle in a state ##0.6|\uparrow\rangle+0.8|\downarrow\rangle##. The apparatus measure it in the ##\sigma_z## basis. Then the observer sees the result. According to...

Hello, Looking for some help on this one! As I understand it, most many world interpretations explain the interference after the slit experiment as weak interference between seperate universes / branches before they decohere (I know not everyone finds it helpful to use the term 'universes' but...

Key points from literature: 1. Scale-dependent decoherence: Studies indicate that decoherence processes can vary significantly across different scales [1]. 2. Hierarchical quantum-to-classical transition: Classical behavior may emerge from cumulative decoherence effects across multiple scales...

Hello everyone, In light of this recent paper, I have some questions. I'm trying to deepen my understanding of information loss in the contexts of time dilation and quantum decoherence and would appreciate some insights grounded in established physics theories. Time Dilation and Information...

In the recent paper "The Decoherent Arrow of Time and the Entanglement Past Hypothesis" by Al-Khalili and Chen, the authors propose that the early universe had very low entanglement entropy, which increases over time and gives rise to the decoherent arrow of time. 1.) Can you elaborate on how...

Isn't the quantum tunneling probability of macroscopic objects always zero due to quantum decoherence? It may be possible in the microscopic world, but I always think it is impossible in the macroscopic world due to countless interactions. Isn't this the same in a universe with infinite time...

I have a couple of questions about decoherence vs. observer wave function collapse and multi-worlds interpretation. Am I right that Zeh's decoherence theory does not involve an observer, and esp not a conscious observer? Also, am I right that his theory does not involve or align with the...

Quantum decoherence. and the emergence of continuous space/time and gravity In another forum I have experienced a lot of combative dialogue asserting that continuous time/space is a property of the smallest Quantum scale. My present knowledge indicates this not true, and that the goal of the...

When I'm teaching Advanced QM, I like to include how to describe some processes in the Heisenberg picture (e.g. double slit) so that a student's thinking isn't overly attached to the "dynamics of the quantum state", but they can also understand effects involving operator evolution. This is a...

Here's the simplest example of decoherence I can think of. (I will drop normalizing factors for ease of typing.) Start with a state ##|\psi\rangle = |0\rangle + |1\rangle##. Measure it in the basis: $$|+\rangle = |0\rangle + |1\rangle, |-\rangle = |0\rangle - |1\rangle$$ It will always...

Hi Pfs, I wonder if in quantum mechanics the question "Did this event occur?" has a yes or no answer like in classical phyics or in our daily life. We are accustomed to consider linear superpositions of states like "dead" and "alive" but id "dead" is a state the death of the cat is an event. i...

A macroscopic object has the order of Avogadro’s number of particles. That’s over 10^23. So the probability of all of them tunneling, at the same time, is on the order of that original small probability, to the 10^23 power. And then on top of that, you have to factor in the chances of it...

Suppose there are two entangled particles A and B, separated by a few miles or light years. If the spin for particle A is observed, then from my understanding, A will experience quantum decoherence. And now we can be sure that B will have the opposite spin since B is entangled with A. Assuming...

I have tried to study decoherence theory for a while now, and it does seem to answer why classical distributions arise, instead of quantum ones.Is this fully accepted as an explanation for a classical world out of a quantum one?

Hello! I read a bit about decoherence lately (I made a post few weeks ago about it and got some reading suggestions) and I would like to try to apply it to a practical situation I need, which is a Penning trap with a single ion at the center. For now I would like to account just for the...

What happens to the other possible outcomes after decoherence has been finalized? Where do they go?

Hello! Assume we have a 2 level system that is in a superposition of its 2 states: $$\psi = \frac{|0>+|1>}{\sqrt(2)}$$ If we put it in a chamber at a given temperature (say that the chamber has perfect vacuum) the system will lose its coherence due to the blackbody radiation from the chamber...

If we have binary decoherence at spacetime location X, as far as I understand, we almost instantly have a splitting into two worlds. Now if we have a different location Y, about a lightyear apart from X, then the decoherence hasn't reached Y before a year has passed. So for Y, the split hasn't...

If quantum objects’ superpositions decohere rapidly due to exposure to a surrounding environment, why have I heard it said that two entangled particles can be a large distance apart while still having undetermined properties? Wouldn’t decoherence occur while the particles were moving apart?

Hi Pf, I take the case of Alice and Bob in the EPR experiment. Here Bob does not measure spin projections but make a Young's double slit experiment. What Alice does on her side will not be known by Bob. She can decide to let her particles go freely to the left (in the environment of Bob). Bob...

If I use the expression ##(|A\rangle+|B\rangle)|M\rangle \rightarrow |A\rangle|M_A\rangle+|B\rangle|M_B\rangle## for decoherence, does that mean that we can infer that, IF the measured value is ##A## that THEN we will measure ##M_A##, OR that IF we measure ##M_A## THEN the measured value must...

Do I have the proper understanding of the following three double-slit experiment situations? #1 While a standard double-slit experiment is run via a Mach-Zehnder interferometer apparatus that completely lacks which-way detectors, can an ordinary human experimenter be present and watch that...

Hello, there. I am studying a model for decoherence of two entangled photons. The space for the first photon is 2 dimensional, while that for the other one is 6 dimensional. In total, the system will be in a 12 dimensional space. Initially, they are set to one of the Bell states, such as...

On page 8, I don't understand the last paragraph. It says if ##|A \rangle = U|0\rangle ## and ##|B \rangle = U|0\rangle ## then ##\langle A | B \rangle = 1##. Of course ##U |0\rangle## is a unique state (##A## and ##B## are the same by this definition). So I assumed what he meant was more...

Couple questions here. 1. What do you think is the best source to read about decoherence, both from an intuitive/high level pov, but also with mathematical details. I'd partially read a recommended paper by Schlosshauer a while back, is that still the bible for this? 2. If probabilities in...

I'm a current high school student and I’m aspiring to become a biochemist. I’m at the moment writing an article about adaptive mutations but there is a lot of tricky quantum mechanics in it which I simply don't get. I have asked everyone and got no answer until someone recommended to ask it in a...

Weinberg says in his book "Lectures on Quantum Mechanics" that the born rule can be deduced from decoherence, and this solves the measurement problem. I'm looking for reference, book or article, to understand this better. Thank you

Generally, what physical process causes loss of quantum coherence? Is it known?

The answer is no and even when decoherence occurs for Wigner's Friend in the lab, quantum coherence remains. Let's start with the paper that illustrates this. Assisted Macroscopic Quantumness CONT. https://arxiv.org/abs/1711.10498 Wow, I recently read this paper and the results are simply...

Is the reason you can make out the shape of the sun and the moon is because the gaps between the leaves cause the light to be photons instead of waves?

Would this be an accurate portrayal of measuring the spin of an electron with a SG detector?: The electron is in a superposition of spin-up and spin-down; Upon entering the magnetic field of the SG detector, the electron enters a superposition of an upward trajectory and a downward trajectory...

I'd like to draw attention to the recent survey M. Schlosshauer, Quantum decoherence, Physics Reports (2019). Available online 18 October 2019

I have a single technical question regarding a statement on page 7 of the paper "Dynamical quantum correlations of Ising models on an arbitrary lattice and their resilience to decoherence". The paper up until page 7 defines a general correlation function ##\mathcal{G}## of a basic quantum Ising...

This question is inspired by a comment that @thephystudent made where he said that "The dephasing between the Bragg pulses is not unitary, I believe it can be explicitly written in Lindblad form and generates heat. I believe this Point of view is the same as (among others) the papers of...

Something puzzling and inconsistent. Decoherence was supposed to remove the need for observers in Copenhagen. But how come Lee Smolin didn't discuss anything about decoherence with regards to the Copenhagenists but only the Everettians in his book "Einstein Unfinished Revolution: The Search for...

My question is about decoherence, specifically in regards to its interpretation in Hilbert space. In every single textbook I've read, decoherence has always been explained by (1) introduce density matrix and (2) explain that interactions with environment cause off-diagonal terms (coherences)...

This thread is a direct shoot-off from this post in the Insights thread Against "interpretation" - Comments. I am usually not a big fan of Ballentine, but I tend to fully agree with him on the following issue (taken from this paper, credits to @bhobba) Decoherence theory is a pragmatic...

This is based on the Hugh Everetts interpretation of quantum mechanics, where the waveform never collapses but the observer becomes a part of it, thus experiencing decoherence of the wave form from their point of view. So, let's say someone is doing the two-slit experiment. The particles going...

I just read an excerpt from Philip Ball's new book and was disappointed by its hyperbolic, boosterish tone. He adopts the pose that physicists have made great strides in understanding what happens during measurement. Wave functions decohere, etc. He concludes by saying something like "now...

In Wikipedia's outline of the Many Worlds Interpretation of quantum physics https://en.wikipedia.org/wiki/Many-worlds_interpretation, it states "In many-worlds, the subjective appearance of wavefunction collapse is explained by the mechanism of quantum decoherence,...", yet I thought decoherence...

Hello, I am studying the entanglement in quantum physics, especially the Aspect's experience where 2 photons initially correlated keep this correlation through the measure of their polarity. The Wikipedia article is only available in French, but there is an article in English written by Alain...

Homework Statement In Gerry's book "Introductory quantum optics", Chapter 8.5 Decoherence, Page 207, there is a calculation which doesn't give the detail derivation, who can give me the calculation from (8.26) to (8.27)? Homework Equations The coherent state is defined by...

Before quantum mechanics, light was generally seen as a wave and matter as particles (biliards). From e.g. the discovery of the photoelectric effect, one saw that light can also be seen as a particle. From e.g. the double slit experiment, one makes the interpretation that matter can also be seen...

Suppose we have a quantum system ##Q## with an initial state ##\rho^{(Q)}##. The measurement process will involve two additional quantum systems: an apparatus system ##A## and an environment system ##E##, hence giving the initial state of the system ##\rho^{(AEQ)} = \rho_{0}^{(AE)}\otimes...

I have two questions about the following type of scenario: We have a laser sending photons through the usual double slit apparatus giving us the usual interference pattern, except that now we introduce some physical matter (that are not photons) that the photons will interact with before going...

Good evening! I know, that the questions similar to mine were frequently asked in this forum. Recently I even saw the thread about macro-realism and was satisfied by the answer to it. However, one article made me try to find some clarification. The link to the article...

According to decoherance. Say there is a pure state initially in state: |ψ⟩=α|0⟩+β|1⟩ After decoherance (interaction with environment), the system will transform into the improper mixed state of: ρ=|α|2|0⟩⟨0|+|β|2|1⟩⟨1| This is the "apparent" collapse that decoherance refers to. With the...

If the particle is undisturbed in the two slit experiment, an interference pattern will show up. The weird quantum behavior here is that the particle can have "negative probabilities" associated with its position and momentum, thus they can cancel each other and form the pattern we see. When...