Can the quantum state of an electric current change its outcome?

[MirceaKitsune]

Low mass particles, including electrons and photons, are subject to the laws of quantum physics. Earlier I was pondering the nature of electricity, and how quantum mechanics could play various roles in the behavior of electric currents. I became curious about one possibility, which might be of interest to the development of quantum computers or understanding how the brain and its neurons work: Can you have a circuit where an electric current might choose a different path based on its quantum state? I'm curious for both standard electronics as well as electrochemical circuits.

 

In regard to electronic devices, I'm wondering if a circuit can be designed to redirect electrons based on their quantum state. For instance: You have a wire that splits into two wires. If an electron is in one quantum state when it reaches the junction point, it goes through the left wire... while if it's in another quantum state, it goes to the right. A more practical and concrete example would be: You have a single wire separated by a non-conductive obstacle, but which is thick enough to allow particles to tunnel through. If an electron that reaches this obstacle manages to tunnel, it's taken by the remaining wire and continues its journey... while if it doesn't, it stops there and does not pass.

 

For electrochemical signals, I'm not fully sure where to direct my question, since I'm still not fully familiar with them and still learning about action potentials and electrolytes. But in essence, I'm curious if the quantum state of particles involved in transmitting the electrical signals can determine the outcome, from what's known so far. Could a quantum leap in an ionized particle cause a different neuron to fire, or the signal to reach or not reach a neuron? Or do quantum physics play no role in the path neural signals take?

[studiot]

What do you understand a quantum state to be, particularly with reference to electric currents?

[MirceaKitsune]

What do you understand a quantum state to be, particularly with reference to electric currents?

 

In my case at least, I think of it as the location a particle has based on quantum probability. If an electron takes a quantum leap, it goes into a different state and changes orbit. I thought that was a mainstream term, sorry for omitting it from the first post.

[Strange]

In regard to electronic devices, I'm wondering if a circuit can be designed to redirect electrons based on their quantum state.

 

Sounds like spintronics.

 

In my case at least, I think of it as the location a particle has based on quantum probability. If an electron takes a quantum leap, it goes into a different state and changes orbit.

 

Or maybe not. Normal semiconductors depend on the controlling the energy levels of electrons for their behvaiour.

[studiot]

I asked because a 'quantum state' is defined by a characteristic list of quantum numbers.

 

So a different state is entered when one of those numbers change.

That is what Strange was referreing to when he saud 'spintronics' - The spin quantum number.

 

However the charges in electric current in conductors is delocalised. That means they are no longer in orbitals that belong to individual atoms, they belong to what amounts to super orbitals that encompass the whole conductor, split or not.

 

That means that the quantum number defining the orbital does not change wherever the electron is in the conductor, ie it does not change with position.

 

Please note this is a very crude, non mathematical, description to help understanding.

[MirceaKitsune]

Oh, the spin can matter too. I was only thinking about position for some reason, and missed the fact that electrons have spin too. Basically, any change that's attributed to quantum physics and of quantum nature counts in my question. I'll also google about spintronics.

Edited August 16, 2014 by MirceaKitsune

[studiot]

Spin is irrelevent to the super orbitals.

 

Electrons (and holes) obey the Pauli Exclusion principle which basically says that no two coupled electrons ie in the same orbital can have the same set of quantum numbers.

 

What happens is that all the quantum numbers that define energy levels are very close together and form what is known as an energy band so the delocalised electrons occupy these states.

 

That is what Strange meant by talking of controlling energy levels.

 

So in effect, the electrons already do what you are suggesting, because they move about freely within the energy band.

We do not have the ability to define the very fine levels within the band.

[Enthalpy]

Spin is irrelevent to the super orbitals.

 

Electrons (and holes) obey the Pauli Exclusion principle which basically says that no two coupled electrons ie in the same orbital can have the same set of quantum numbers.

 

Spin still exists in metals and semiconductors. This enables spintronics, permits two electrons in otherwise the same state, and does influence the occupation statistics.

[studiot]

The current state of 'spintronics' is that it is somewhere between wishful thinking and a gleam in its parents eyes.

 

That does not mean it might one day become useful.

 

http://www.cam.ac.uk/research/news/superconducting-spintronics-pave-way-for-next-generation-computing

 

My discussion was firmly based on current (pun intended) practice.

Edited August 17, 2014 by studiot

[MirceaKitsune]

Thanks for the additional info. I'm still confused about one thing though: Aren't quantum physics posing an obstacle to spintronics? From what I'd expect, an electron would unpredictably leap between different states in which it spins differently. Unless of course, the spin of the electron in all of these states is polarized.

[studiot]

Spin is not polarised it has one of two quantum values +1/2 or -1/2.

 

Quantum spin in Fermi bands (non localised orbitals) is not yet well studied so I repeat, it may happen in the future.

[Strange]

Thanks for the additional info. I'm still confused about one thing though: Aren't quantum physics posing an obstacle to spintronics? From what I'd expect, an electron would unpredictably leap between different states in which it spins differently. Unless of course, the spin of the electron in all of these states is polarized.

 

Electrons don't randomly switch between spin states; it takes energy to change it. This is (in my very limited understanding) how a spin based memory would work: each cell would contain an electron in either spin up or spin down representing 1 and 0.

 

Note that other quantum effects are used in various devices. For example, flash memory depends on tunnelling to get charge into and out of a "floating" (isolated) gate electrode.

[studiot]

 

Electrons don't randomly switch between spin states; it takes energy to change it.

 

Yes, that's right. there is reference to this in the literature and that is why even with superconductors there is no free lunch on this.

But it may be much faster and more compact.

 

So Microsoft will be able to reach new heights of computing inefficiency when they get all to exabytes to waste.

 

[Enthalpy]

Spin is not polarised it has one of two quantum values +1/2 or -1/2.

 

Quantum spin in Fermi bands (non localised orbitals) is not yet well studied so I repeat, it may happen in the future.

 

The spin values can be prepared to be definite. This permits spintronic devices to show some effects right now; whether we get operating and useful chips some day is a matter of technology, not of theoretical limits.

 

 

Every hard disk drive for several years uses a magnetic read sensor based exactly on electron spin in metals, through the giant magnetoresistive effect. At least this one is present technology.

 

 

The spin in energy bands is perfectly understood and simple theory. It works exactly like anywhere else: two electrons per otherwise identical state. This was included in semiconductor theory right from the beginning, and is necessary to compute the filing of the bands. It's even necessary for atoms to stay together in a piece of metal.

 

[studiot]

 

Every hard disk drive for several years uses a magnetic read sensor based exactly on electron spin in metals, through the giant magnetoresistive effect. At least this one is present technology.

 

 

 

So it is already in use.

 

Thank you I have learned something. +1

[MirceaKitsune]

Yeah, lots of stuff I didn't know either. Hopefully this can be understood and used even more effectively over time.

 

Otherwise I'm still curious about my second question as well, even if it's a slightly different idea; Are neurons spintronics to any extent? Does the electricity traveling through the brain depend on quantum state and / or spin polarization? Does the current having a different quantum property make it reach other neurons? Are quantum physics or quantum leaps involved in how the mind works and takes decisions?

 

I'm more confused here because from what I know, electrochemical signals and action potentials don't involve electrons. Maybe someone can also correct me here and explain this better.

[studiot]

You need a biophysicist for that one.

[Strange]

I'm more confused here because from what I know, electrochemical signals and action potentials don't involve electrons. Maybe someone can also correct me here and explain this better.

 

The electrical signals in neurons do not travel as electrical currents - which may be what you are thinking of. It is a much more complex biochemical process. There are structures in the cell membrane that can pump ions in and out out the cell. Nerve impulses are transmitted as a "cascade" of these ion pumps along the length of the neuron.

 

At the end of a neuron, this causes the release of various chemicals which stimulate the surrounding cells to fire (or not).

[Enthalpy]

Because we observe brain activity through electric signals (EEG) many sources claim brain's activity to be an electric one, but it's chemistry, and electric signals are a by-product..

 

Chemistry is complicated, biochemistry more so...I expect most molecules and ions to have paired electrons, and even when not, the spin of a lone electron is probably not what influences the emission and capture of a neurotransmitter. But, well, we still discover unknown neurotransmitters presently.

 

Giant magnetoresistance:

http://en.wikipedia.org/wiki/Giant_magnetoresistance

Edited August 19, 2014 by Enthalpy