The quantum realm is incredibly fascinating but can be difficult to visualize. Washington State University physicists share a few tangible insights.
Michael Forbes, associate professor of physics and spokesman for the WSU Quantum Initiative says quantum’s advantage over classical Newtonian physics comes down to the phenomena called entanglement and superposition.
“This is a weird thing in quantum mechanics,” he says. “You can have a pair of quantum particles that spin in such a way that one points up and the other points down. Entanglement is the idea that they always have to point in opposite directions—if you measure one to be up, you are guaranteed to measure the other to be down.
“But until you measure them, they can be in what is called superposition of both up and down. You don’t know—and quantum mechanics says no one can know—which spins they have until you make a measurement. Only after the measurement will both point in a particular pair of opposite directions.
“Superposition has troubled physicists like Schrödinger who illustrated the absurdity with his idea of a cat in a box,” says Forbes. “The box has a vial of poisonous gas, which will be triggered if the spin is pointing up but not if the spin is pointing down. Until you make a measurement, the cat is in a superposition—simultaneously both dead and alive.
“Although entanglement and superposition have been tested to high precision for small systems, how they apply to large objects like cats is still a mystery.
“In principle, you can take one particle to the moon and leave the other on Earth,” he says. “And, until you measure them, no one can know which way they point, only that they’ll still be pointing in opposite directions.
“A similar concept was adopted during World War II when spies used a one-time pad with a string of random numbers to encrypt messages for the government. Only the government and the spy would have the string of numbers, and if they were truly random no one could break the code.
“In other words, if you take your quantum system and be careful not to measure it, you know you have opposite spins in your particles,” says Forbes. “You give one spin to your spy and you keep the other. When you have to encode a message, you measure the spin and use that value to code the message. So, theoretically, you now have perfectly random numbers to encrypt it. In addition, beyond what is possible with one-time pads, no one can read the code without your knowledge. This is the basis for quantum cryptography.”
Brian Saam, professor and chair of the department of physics and astronomy, is an experimental physicist who studies spin systems as well as hyperpolarized noble gases like xenon and helium.
“One of my favorite quantum studies involves MRI—magnetic resonance imaging for medical diagnostics,” he says. “The images come from the fact that water molecules contain hydrogen atoms which have a proton in the nucleus with something called spin. These protons act like small magnets.
“In simple terms, the MRI manipulates those magnets to generate currents like a generator in a power plant. This creates a signal that is used to create the diagnostic image.
“It means the MRI works really well when there’s water in the subject being imaged and humans are about 80 percent water,” Saam says. “The beautiful thing is that if you look at a knee joint, instead of only seeing bone as with an X-ray, you’ll see bone, tendon, cartilage, and fat—all show up differently as all have different water contents.
“The problem with MRI is that it doesn’t work well in the lungs as most healthy lungs contain little water,” he says.
Saam uses a laser to align the nuclear spins of ordinary noble gases, and once prepared in this way, the hyperpolarized gas becomes very sensitive to magnetic resonance and can be inhaled for imaging purposes.
“Normally, the gas wouldn’t show up as it is so much less dense than a liquid,” he says. “But if I treat it optically and align all the magnets, the gas shows up on the MRI. You can actually see it moving through the lungs in real time.
“So, it’s a way of extending MRI technology to an organ that you wouldn’t otherwise be able to image.”
Professor Steve Tomsovic is a theoretical physicist who studies the extraordinary field of quantum chaos.
“We often talk about quantum mechanics when we talk about the microscopic world—and classical physics with the macroscopic world,” he says. “There’s kind of a frontier in between those two worlds where you can find both classical and quantum properties.
“It’s our goal to search for new phenomena associated with these quantum systems due to chaos. For example, we might see things like chaos-assisted tunneling.”
Typical tunneling is a quantum effect where particles can pass through normally impenetrable barriers.
“When you look at a coffee cup, the coffee particles stay inside the cup, they don’t go through the walls,” says Tomsovic. “But if it was a quantum coffee cup, the particles would leap through the walls, they’d find their way outside the cup. That’s tunneling.
“It’s like fission in atomic nuclei which makes nuclear weapons possible. The particles are bounded but can still escape. So, the radioactivity behind nuclear fission involves tunneling processes.”
Tomsovic says chaos-assisted tunneling is radically different. “You see far different types of behaviors than normally expected. It’s just a different realm of phenomena.”
On another note, he offers an interesting look at the role of entanglement in quantum teleportation, which he says is theoretically possible.
“The qubits on which quantum computers are based can be moved to a new location in exactly the same state without moving any matter,” says Tomsovic.
“Quantum teleportation is a little like the transporter in Star Trek. The state of a qubit in one location is destroyed but reconstructed exactly in another qubit elsewhere.
“In Star Trek, when they step onto the transporter, they disappear. Then, wherever they showed up, that was a total new them in exactly the same state.”
Though teleportation has been achieved with atoms, Tomsovic says it will be a very long time, if ever, before it will work on large complicated systems like humans.
Read more about quantum mechanics and WSU research.