Physicists Measure Elusive 'Persistent Current' That Flows Forever

Oct 08, 2009
Physicists Measure Elusive 'Persistent Current' That Flows Forever
Harris made the first definitive measurement of an electric current that flows continuously in tiny, but ordinary, metal rings. (Photo: Jack Harris/Yale University)

(PhysOrg.com) -- Physicists at Yale University have made the first definitive measurements of "persistent current," a small but perpetual electric current that flows naturally through tiny rings of metal wire even without an external power source.

The team used nanoscale cantilevers, an entirely novel approach, to indirectly measure the current through changes in the magnetic force it produces as it flows through the ring. “They’re essentially little floppy diving boards with the rings sitting on top,” said team leader Jack Harris, associate professor of physics and applied physics at Yale. The findings appear in the October 9 issue of Science.

The counterintuitive current is the result of a quantum mechanical effect that influences how electrons travel through metals, and arises from the same kind of motion that allows the electrons inside an atom to orbit the nucleus forever. “These are ordinary, non-superconducting metal rings, which we typically think of as resistors,” Harris said. “Yet these currents will flow forever, even in the absence of an applied voltage.”

Although persistent current was first theorized decades ago, it is so faint and sensitive to its environment that physicists were unable to accurately measure it until now. It is not possible to measure the current with a traditional ammeter because it only flows within the tiny metal rings, which are about the same size as the wires used on computer chips.

Past experiments tried to indirectly measure persistent current via the magnetic field it produces (any current passing through a metal wire produces a magnetic field). They used extremely sensitive magnetometers known as superconducting devices, or SQUIDs, but the results were inconsistent and even contradictory.

“SQUIDs had long been established as the tool used to measure extremely weak magnetic fields. It was extremely optimistic for us to think that a mechanical device could be more sensitive than a SQUID,” Harris said.

The team used the cantilevers to detect changes in the magnetic field produced by the current as it changed direction in the aluminum rings. This new experimental setup allowed the team to make measurements a full order of magnitude more precise than any previous attempts. They also measured the persistent current over a wider range of temperature, ring size and than ever before.

“These measurements could tell us something about how electrons behave in metals,” Harris said, adding that the findings could lead to a better understanding of how qubits, used in quantum computing, are affected by their environment, as well as which metals could potentially be used as superconductors.

Authors of the paper include Ania Bleszynski-Jayich, William Shanks, Bruno Peaudecerf, Eran Ginossar, Leonid Glazman and Jack Harris (all of Yale University) and Felix von Oppen (Freie Universität Berlin).

Provided by Yale University (news : web)

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User comments : 16

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Sean_W
1 / 5 (1) Oct 08, 2009
How often does the curent change direction? Does it do that spontaneously or in reaction to noise in the environment?
ruebi
not rated yet Oct 08, 2009
Is there a difference between persistent current and perpetual motion? The later is said impossible to exist but that is what this story made me think about.
Bob_Kob
not rated yet Oct 08, 2009
Well I think if you try to do any work, the current will stop.
brant
not rated yet Oct 08, 2009
Well I think if you try to do any work, the current will stop.


I suspect you could do work, stop, the current would return and then do some more work.
Since it is there in the first place(where does it come from?), why would it disappear for good?
magpies
Oct 09, 2009
This comment has been removed by a moderator.
devanate
Oct 09, 2009
This comment has been removed by a moderator.
lengould100
5 / 5 (1) Oct 09, 2009
If Brant were correct, where would the extracted power be coming from? Thermal input?
DraganGlas
5 / 5 (1) Oct 09, 2009
Greetings,

@brant/lengould100
...

Since it is there in the first place(where does it come from?), why would it disappear for good?


The counterintuitive current is the result of a quantum mechanical effect that influences how electrons travel through metals, and arises from the same kind of motion that allows the electrons inside an atom to orbit the nucleus forever. “These are ordinary, non-superconducting metal rings, which we typically think of as resistors,” Harris said. “Yet these currents will flow forever, even in the absence of an applied voltage.”


It's similar to the molecular bonds of carbon atoms in benzene - they "flicker" between single- and double-bonds.

Here, as the article indicates, it's due to the passage of electrons (which is basically what an electrical current comprises) between atoms throughout the ring of metal.

Kindest regards,

Dragan Glas
DraganGlas
not rated yet Oct 09, 2009
Greetings,

@brant/lengould100
...

Since it is there in the first place(where does it come from?), why would it disappear for good?


The counterintuitive current is the result of a quantum mechanical effect that influences how electrons travel through metals, and arises from the same kind of motion that allows the electrons inside an atom to orbit the nucleus forever. “These are ordinary, non-superconducting metal rings, which we typically think of as resistors,” Harris said. “Yet these currents will flow forever, even in the absence of an applied voltage.”


It's similar to the molecular bonds of carbon atoms in benzene - they "flicker" between single- and double-bonds.

Here, as the article indicates, it's due to the passage of electrons (which is basically what an electrical current comprises) between atoms throughout the ring of metal.

Kindest regards,

Dragan Glas
DraganGlas
Oct 09, 2009
This comment has been removed by a moderator.
otto1923
not rated yet Oct 09, 2009
it's due to the passage of electrons (which is basically what an electrical current comprises) between atoms throughout the ring of metal.
And yet it runs forever, nothing degrades. Where does the power COME from? Where does the charge on an electron come from, and why doesnt it degrade even when the electron does work? Not the vacuum please; thats like saying out of thin air, or out of your butt. People use these theories as approximations to a certain level, but they still cannot EXPLAIN them. Leaves questions open on scalar physics and zero-point energy.
SincerelyTwo
not rated yet Oct 09, 2009
Maybe it does degrade, but at a rate we cannot reliably measure.

Besides, perpetual motion and this persistent current don't break the laws of physics, they don't produce excess energy, what you put in is what you have - and what you have just continues to remain in the state that it's in until you interfere.

You can only minimize the amount energy in a system degrades, maybe removing friction entirely in some controlled experiments or in some unique environments in space. But you can't make there be SO LITTLE friction that you get... INVERTED FRICTION and suddenly the system radiates energy for no freaking reason.

The problem with all of this is failure to understand and communicate on the topics with clear understanding of terminology. Most people say these things implying excess energy, when objectively from the math it just means lack of friction or degrading forces..
otto1923
Oct 09, 2009
This comment has been removed by a moderator.
ChiefOctopus
Oct 09, 2009
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zevkirsh
3 / 5 (1) Oct 09, 2009
millions upon millions is being invested in all the roomtemperature superconducting material research.

it is counterintuitive, but solving the puzzle of the 'persistent' current (as in this article) is going to be a small, yet INTEGRAL, part into making a room temperature superconductor possible

the big part of the superconducting puzzle is the geometry of the magneto-electrical strucuture of a material. HOWEVER....a another small part of the puzzle is about the freedom of unbound electrons to move through a medium containing an amount of bound electrons. and it lies in this research. unfortunately ...all the superconducting researchers don't yet realize that this area is actually worth a small amount of their time....

it's about thinking 'out' of the box.

sender
not rated yet Oct 09, 2009
Using these rings in series-parallel switched arrays should make for some extremely powerful antennas.
johanfprins
1 / 5 (1) Oct 10, 2009
Was an external magnetic-field applied to initiate the persistent current? In the case of a superconducting ring one first have to apply a magnetic-field; One can then switch off the magnetic field and the current with its trapped Lenz field will persist.
eurekalogic
not rated yet Oct 11, 2009
Its Teslas Ether.
NotAsleep
not rated yet Oct 13, 2009
To create information requires energy. The cantilevers got that energy from somewhere. I'll bet the actual scientific article would mention something about the current decreasing proportionally to the energy expended in moving the cantilevers. Unfortunately, I can't find it on the Science Magazine webpage. If anyone finds a link to that article, please post here!
DraganGlas
not rated yet Oct 13, 2009
@NotAsleep

Here you go...

http://www.scienc...5950/275

Kindest regards,

Dragan Glas
NotAsleep
not rated yet Oct 14, 2009
Thanks, DraganGlas, although that link seems to go to a different article on the hubble... I DID end up finding the article but t'isn't free and I t'isn't rich enough to afford REAL science articles

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