Entanglement and the double slit experiment

Is the double slit experiment an example of entanglement when it seems as if the photon is going through both slits? Or put another way, is it at this stage when we attempt measurement we see a photon on one side affect the photon on the other side? Do entangled particles have to be made … Read more

A foundational question about entanglement

The recent Nature article http://www.nature.com/news/data-teleportation-the-quantum-space-race-1.11958 prompts me to ask this question, which is of the same tenor as that asked at the recent Perimeter Institute meeting attended by Zeilinger et al., i.e. “Do the pairs somehow communicate though some still-unknown information channel?” It seems to me that entanglement could be described as behaving as if … Read more

Why use 2 nonlinear crystals in conjunction for SPDC?

I’ve seen a few articles (ex: 1, 2) that use either two BBO crystals consecutively or a BBO and a KDP crystal to create entangled photon pairs from Spontaneous Parametric Down-Conversion (SPDC). And from this answer, I understand that it’s used as a trick because type I conversion doesn’t produce entangled photons. I just don’t … Read more

Correlation vs. entanglement for composite quantum system

Some authors exclusively use “Correlation” to classify composite quantum states, whereas most only speak of “Entanglement”. Correlation basically means that measurements on the subsystems are stochastically dependent and entanglement means non-separability of the composite state. I am wondering, are those classifications equivalent, or is there any hierarchy (e.g. if a composite state is non entangled, … Read more

How is China’s ‘Quantum Satellite’ going to send information through entangled photons? – no-communication theorem

So I recently read a news article about how China is using Quantum entanglement to send information. Now I thought this was very strange because I know for a fact that you cannot use quantum entanglement to send information through the entangled pair of objects. (See No-communication theorem). How are they using entanglement to send … Read more

Unitarily evolving a separable state into an entangled one

We consider two spin 1/2 systems that are described by the following Hamiltonian: H12=jZ1⊗Z2 The composite system is initialised in the state: |ψ12(0)⟩=|x+,x+⟩, which written in the z basis (z+ being spin up state along the z dimension), is: |ψ12(0)⟩=1/2(|z+,z+⟩+|z+,z−⟩+|z−,z+⟩+|z−,z−⟩). Given the Hamiltonian in (1), the unitary time evolution is U(t)=e−iH12t/ℏ, and after a time … Read more

How are two-qubit states experimentally projected into the Bell basis?

To perform Quantum Teleportation, we need state of two entangle qubits in the Bell basis (|00⟩+⟩11⟩√2,|00⟩−|11⟩√2,|01⟩+|10⟩√2,|01⟩−|10⟩√2). To project in the product basis (|00⟩,|10⟩,|01⟩,|11⟩, or in the product basis along x or y axis (or any other axis)) we can check whether the individual spins are pointing up or down, but I don’t know how the … Read more

Quantum entanglement and information transfer: Does particle separation process set speed limit?

Background I recently read that a group had managed to overcome both the communication loophole and the detection loophole for Bell’s theorem. In reading the article, I started to think about another issue which I had not realized upon first learning about quantum entanglement. I am aware that entanglement does not necessarily mean one can … Read more

When does the world split in MWI

I’ve been reading Eliezer Yudkowsky’s blog post regarding decoherence and many worlds, and although he is not a physics but a strong proponent of MWI, I can basically see why he feels that MWI is a “simple” explanation. However, in all the posts there it’s decoherence that’s the natural (and mathematically simple) approach to QM, … Read more

Quantum entanglement definition [closed]

Closed. This question needs details or clarity. It is not currently accepting answers. Want to improve this question? Add details and clarify the problem by editing this post. Closed 6 years ago. Improve this question How can we define Quantum entanglement (in QFT)? What are the known mathematical settings and special physical (or logical) conditions … Read more