Just recently, researchers managed to “entangle” two very tiny aluminum drums as if they were merely quantum particles — a first that helps pave the way for quantum computing. But it’s an unsettling first because the world above the level of the electron (macroscopic world) is supposed to behave according to Newton’s classical physics rules, not weird quantum rules under which two entangled particles sync no matter how far apart they are (non-locality).
Like conductors of a spooky symphony, researchers have ‘entangled’ two small mechanical drums and precisely measured their linked quantum properties. Entangled pairs like this might someday perform computations and transmit data in large-scale quantum networks.National Institute of Standards and Technology (NIST), “Quantum drum duet measured” at ScienceDaily (May 6, 2021) The paper is closed access.
As a writer at Nature puts it,
The findings, described in two Science papers on 6 May, could help researchers to build measuring devices of unprecedented sensitivity, as well as quantum computers that can perform certain calculations beyond the reach of any ordinary computer.Davide Castelvecchi, “Minuscule drums push the limits of quantum weirdness” at Nature
Mind Matters News asked experimental physicist Rob Sheldon for some comments on one of the papers:
This paper is probing the boundary between the quantum mechanics (QM) world and the classical world.
Almost a century ago in 1924, when the QM world was being explored, Louis deBroglie (1892–1987) suggested that even atoms could behave like waves, with a wavelength proportional to Planck’s constant divided by momentum.
The general consensus was that electrons might have wavelengths we could measure (because their momentum was small). But the wavelength of atoms would be much much shorter, and of course, that of molecules and Volkswagens would be too short to ever measure. This expectation led to a dividing wall between the microscopic QM world and the macroscopic “classical” world.
Erwin Schrödinger (1887–1961) then proposed his famous “live/dead cat” thought experiment, to show that QM could still have macroscopic effects. His point was that “waves” and “wavelength” are only one aspect of QM. There are also effects like “interference” and “collapse of the wavefunction,” which is what killed Schrödinger’s cat.
These effects, noticeable in the macroscopic, classical regime, show that this dividing wall has windows. Perhaps a better example of everyday QM, is the “doping” of silicon to generate non-local electron waves that we call “conduction bands,” which enable silicon to “turn on and turn off” the flow of electricity in a transistor. And those transistors are what make your smart phone smart, instead of just a chunk of pretty quartz.
But despite the harnessing of QM in many macroscopic everyday items, there has been a small contingent of physicists who don’t want simply to open a window, but rather move the entire wall.
Moving the wall
Eighty years ago, Stern and Gerlach made “beams of single atoms” by heating silver in a crucible with a tiny hole that allowed a stream of hot silver atoms to boil out. They then showed that the atoms possessed QM spin.
Thirty years ago, Pritchard cryogenically cooled sodium atoms to “entangle” them. He showed that he could make two streams behave as a “double slit” interference pattern. The atoms behaved as waves — just as deBroglie had argued.
Molecules soon followed. And then the race was on to see who could make the heaviest object behave as a wave.
In the recent experiment, the group at NIST had about a trillion aluminum atoms in a microscopic “drumhead” that bends up and down like a drum when they shine microwaves of the same frequency on it.
They connected two drums together with a microwave waveguide. Then, like Pritchard, they cooled their drums down to eliminate random shaking from hot atoms, pinged them with a microwave pulse to start them vibrating, and looked to see if their vibrations are talking to each other. They claim that it takes lots and lots of statistics, but after all the random stuff is smoothed out, the trillion or so atoms are syncing up with each other in ways that cannot be classical.
The result? We now have evidence that we can coherently treat a trillion aluminum atoms as a single wave. The wall between QM and classical has moved, and nearly naked eye visible objects can be turned into waves.
Why is this important?
Well, the atom beam technology that vindicated deBroglie in 1991 was immediately set to work to make super-sensitive detectors. Likewise the technology developed in 2021 and described here is expected to show up in QM computers.
That is, if our electronic computers were using quantum waves or “qubits” instead of using 1’s and 0’s, or “bits,” then some calculations that take a very long time with bits could be solved quickly with qubits. Like cracking the algorithm that encrypts your secure emails. But qubits evaporate really fast, and they are hard to measure — so if we can store them on trillion-atom drums, we would have a long-lived, easy-to-measure way to store qubits. Of course, there are a dozen competing qubit technologies that may work better than drums, but at least in history books, moving the wall will last forever.
You may also wish to read:
In quantum physics, “reality” really is what we choose to observe Physicist Bruce Gordon argues that idealist philosophy is the best way to make sense of the puzzling world of quantum physics. The quantum eraser experiment shows that there is no reality independent of measurement at the microphysical level. It is created by the measurement itself.