Changing the spin of a Quantum particle

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    Particle Quantum Spin
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Discussion Overview

The discussion revolves around the manipulation of the spin of quantum particles, particularly in the context of quantum communication. Participants explore methods for affecting spin without destroying the particle or inducing randomness, and consider the implications of entanglement on these methods.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant inquires about methods to meaningfully affect the spin of a quantum particle, specifically in relation to quantum communication.
  • Another participant suggests using a magnetic field to manipulate particles with a magnetic moment, such as electrons, and mentions the use of electric fields for quantum dots, noting the complexity involved.
  • A question is raised regarding whether entanglement affects the feasibility of manipulating the spin of particles.
  • A response indicates that entanglement does not hinder manipulation as long as no measurement is performed, explaining the use of "pi-pulses" and the Bloch sphere for visualizing state manipulation.
  • One participant mentions that wave plates can shift the polarization of photons without disrupting their entangled state, referencing their application in Bell tests.
  • A later post questions the potential for faster-than-light (FTL) communication using polarization states to convey binary information, suggesting a possible link between polarization and communication methods.

Areas of Agreement / Disagreement

Participants express varying viewpoints on the methods of manipulating quantum spins and the implications of entanglement, indicating that multiple competing views remain. The discussion on FTL communication also introduces uncertainty regarding the feasibility of such a method.

Contextual Notes

Some assumptions about the nature of quantum states and the effects of entanglement on manipulation methods remain unresolved. The discussion does not clarify the mathematical or experimental limitations of the proposed methods.

Who May Find This Useful

Individuals interested in quantum mechanics, quantum communication, and the manipulation of quantum states may find this discussion relevant.

Ikirak
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I've been trying to find out if some one has found a way to meaningfully effect the spin of a
quantum particle in such a way that it didn't destroy the particle or make the spin random. If I'm not being very clear, it may help to tell you I'm thinking about Quantum communication.
Also, I am self taught, so if my understanding of the quantum state is grossly wrong, be kind.
Ikirak
 
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Well, if the particle has a magnetic moment (e.g. an electron) you can just use a magnetic field. This is how NMR (and many other methods) works.
Some systems (e.g. quantum dots) can also be manipulated using an electric field, although this is somewhat more complicated since the coupling is indirect.
 
Would said particle being entangled effect the feasablity of these methods of manipulation?
 
No, not as long as you are not performing a measurement.
When people talk about manipulating two-level systems (e.g. qubits) using "pi-pulses" etc they are usually referring controlling a quantum system using alternating magnetic fields with a certain frequency (which determines how close you are to being on resonance), amplitude (which sets the Rabi period) and duration (determines how much you are shifting the system).
These manipulations can in the case of a single system be visualised using a Bloch sphere where the position of a vector indicates the state of the systems, using a magnetic field you can then rotate this vector.
This can be generalized to entangled systems as well and is in fact how quantum algorithms that utilize entangled systems are implemented; a quantum gate is in fact usually just a sequence of pulses that somehow manipulates an ensemble of qubits.
 
A wave plate will shift the polarization, and will not end the entangled state of photons. This is applied routinely in Bell tests.
 
Thank you for the information. This clears allot up for me.
 
DrChinese said:
A wave plate will shift the polarization, and will not end the entangled state of photons. This is applied routinely in Bell tests.

So can this not allow FTL communication? Because if left polarization means on (1) and right means off (0), can't you communicate in binary?
 

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