By using a stream of electrons to cause vibrations in a crystal, a team of Dartmouth physicists established a link between the traditionally separate worlds of classical and quantum mechanics in a study published July 1, according to physics professor and head researcher Alex Rimberg. The study, which was published in the journal Nature, is the first to use quantum particles to influence the behavior of macroscopic objects, marking a major breakthrough in the field of physics.
Classical mechanics, first described by Sir Isaac Newton in the 17th century, describes the macroscopic objects that are measurable and observable to the naked eye and that people interact with every day, according to Rimberg. Quantum mechanics, which scientists began to research in the 20th century, describes the behavior of extremely small particles such as electrons, Rimberg said.
"The problem is that we don't know how to connect [classical and quantum mechanics] to each other," Rimberg said in an interview with The Dartmouth. "We don't understand how stuff in the classical world arises out of what we know is going on at the quantum mechanical level."
Rimberg, along with a team of researchers including physics professor Miles Blencowe and graduate student Joel Stettenheim, identified a connection between classical and quantum mechanics by creating movement in a macroscopic metal crystal with a stream of electrons, according to Rimberg.
"We are trying to understand the connection between the microscopic and macroscopic worlds by investigating the properties of objects that straddle in size the two worlds," Blencowe said in an e-mail to The Dartmouth.
The research team which began working in 2007 started the process by sending a stream of electrons through a "tunnel barrier" in a semiconducting crystal, which facilitates the movement of electrons, Rimberg said.
"A tunnel barrier is like if you're standing in front of a wall with a baseball if you don't throw it high enough, it won't go over the wall," he said. "For quantum mechanical electrons there's a different option. If they don't have enough energy to go over the wall, there's a chance they can go through the wall, and this is called tunneling."
Researchers used the movement of electrons through the tunnel barrier to create electrical fields with several different frequencies, and the semiconducting crystal responded by vibrating at its "favored frequency," Rimberg said.
"It's sort of like the semiconductor is a piece of crystal, like a wine glass that if you wet your finger and run it around the rim it starts to vibrate," he said. "It's a resonance in the same being excited by these tunneling electrons."
The vibrating crystal acted as a "piezoelectric object," Rimberg said, or an object which changes shape when it contacts an electrical field.
"There's a huge difference in the size of the [electrons] and the size of the [crystal]," Rimberg said. "It's like taking a flea and putting it on Mt. Everest and having the flea jump up and down and making the mountain move back and forth by meters."
The electrical field was characterized by a difference of approximately 10, 000 electrons, while the crystal was "big enough to pick up with your fingers."
"We live in a classical world, but we know deep down inside everything is quantum mechanical," Rimberg said.
Rimberg said that he will continue to focus on drawing additional connections between the worlds of classical and quantum mechanics. His future work will investigate the chaos theory a phenomenon in classical mechanics which scientists cannot use the initial state of an object to predict its state after a certain time period that has no known counterpart in quantum mechanics.
Rimberg said that he will use the findings of his study in his investigation of a chaotic system that is nonlinear and strongly quantum mechanical.
"It's the kind of stuff that makes you glad you're doing science," Rimberg said. "It's fun to solve the puzzle and it reminds you why you do this stuff because you don't know everything."
Stettenheim did not respond to requests to comment by press time.
