entanglement

If gamblers, investors and quantum experimentalists could bend the arrow of time, their advantage would be significantly higher, leading to significantly better outcomes.

Often when physicists study phases of matter they examine how a solid slab of metal or a cloud of gas changes as it gets hotter or colder. Sometimes the changes are routine—we’ve all boiled water to cook pasta and frozen it to chill our drinks. Other times the transformations are astonishing, like when certain metals get cold enough to become superconductors or a gas heats up and breaks apart into a glowing plasma soup. However, changing the temperature is only one way to transmute matter into different phases. Scientists also blast samples with strong electric or magnetic fields or place them in special chambers and dial up the pressure. In these experiments, researchers are hunting for a stark transition in a material’s behavior or a change in the way its atoms are organized. In a new paper published recently in the journal Physical Review Letters, Barkeshli and two colleagues continued this tradition of exploring how materials respond to their environment. But instead of looking for changes in conductivity or molecular structure, they focused on changes in a uniquely quantum property: entanglement, or the degree to which quantum particles give up their individuality and become correlated with each other.

Chaos. Time travel. Quantum entanglement. Each may play a role in figuring out whether black holes are the universe’s ultimate information scramblers.

In this episode of Relatively Certain, Chris sits down with Brian Swingle, a QuICS Fellow and assistant professor of physics at UMD, to learn about some of the latest theoretical research on black holes—and how experiments to test some of these theories are getting tantalizingly close.

From credit card numbers to bank account information, we transmit sensitive digital information over the internet every day. Since the 1990s, though, researchers have known that quantum computers threaten to disrupt the security of these transactions. That’s because quantum physics predicts that these computers could do some calculations far faster than their conventional counterparts. This would let a quantum computer crack a common internet security system called public key cryptography. This system lets two computers establish private connections hidden from potential hackers. In public key cryptography, every device hands out copies of its own public key, which is a piece of digital information.  Any other device can use that public key to scramble a message and send it back to the first device. The first device is the only one that has another piece of information, its private key, which it uses to decrypt the message. Two computers can use this method to create a secure channel and send information back and forth. A quantum computer could quickly calculate another device’s private key and read its messages, putting every future communication at risk. But many scientists are studying how quantum physics can fight back and help create safer communication lines.

If you’re designing a new computer, you want it to solve problems as fast as possible. Just how fast is possible is an open question when it comes to quantum computers, but JQI physicists have narrowed the theoretical limits for where that “speed limit” is. The work implies that quantum processors will work more slowly than some research has suggested. The work offers a better description of how quickly information can travel within a system built of quantum particles such as a group of individual atoms. Engineers will need to know this to build quantum computers, which will have vastly different designs and be able to solve certain problems much more easily than the computers of today. While the new finding does not give an exact speed for how fast information will be able to travel in these as-yet-unbuilt computers—a longstanding question—it does place a far tighter constraint on where this speed limit could be.

In quantum mechanics, interactions between particles can give rise to entanglement, which is a strange type of connection that could never be described by a non-quantum, classical theory. These connections, called quantum correlations, are present in entangled systems even if the objects are not physically linked (with wires, for example). Entanglement is at the heart of what distinguishes purely quantum systems from classical ones; it is why they are potentially useful, but it sometimes makes them very difficult to understand.

JQI researchers under the direction of Chris Monroe have produced quantum entanglement between a single atom’s motion and its spin state thousands of times faster than previously reported, demonstrating unprecedented control of atomic motion. This work, which may lead to faster and better quantum computer logic gates, is described a recent issue of Physical Review Letters.