01 ~~ Lost inside a strontium-lattice atomic watch
On a bright, sunny day in Oxford, England, 10-year old Alice Dirac was a bit bored visiting her great, great, great grandmother Alice Liddell’s childhood home. She picked up a dusty old book about her namesake’s Adventures in Wonderland and soon nodded off.
The next thing she knew, Alice was awake outside the manor house watching a white rabbit disappear down a rather large rabbit hole after anxiously consulting his pocket watch. Alice ran after him and quickly found herself in a room filled with aggressive playing cards coming straight for her. Without thinking, she took a big swallow from a bottle labeled “drink me,” and as she began to shrink, jumped away from a particularly menacing queen and up into the rabbit’s open pocket watch, which immediately snapped shut.
Alice discovered too late (and to her dismay) that this was not an ordinary pocket watch. Rather, it was a strontium (Sr)-lattice optical atomic pocket watch. Horrified, she realized she had shrunk to the size of one of the 1000 or so Sr atoms keeping the world’s most accurate time.
Hopping up on an atom (which took some doing since it was pretty wavy), Alice realized she wasn’t in Wonderland at all. She had become so small, she was in Quantumland, where everything looks utterly strange and things don’t work at all like they do in the world of normal people. It was also extremely cold, and Alice hadn’t even brought a sweater.
As she watched the atoms around her, Alice noticed some interesting things going on. When two Sr atoms came close enough to touch each other, most of the time they just circled around each other. But, at other times, two Sr atoms crashed right into each other, which is something Sr atoms in the same quantum state aren’t supposed to be able to do.
But then, Alice looked more closely at a pair of atoms in the process of colliding. Their electrons were both in the same coherent superposition of states. They were moving completely in sync, even if they did look more like a wave than a ball. But something was different about these atom crashers: Far inside of each of them was a hard wavy ball, the atomic nucleus, and the nucleus was a different color inside each of the colliding atoms. “Ahha,” Alice reflected, “These two atoms are in different nuclear spin states, or flavors. No wonder they can collide.”
Alice knew there could be up to 10 different spin flavors in the nuclei of Sr atoms. And, even if you cool them down to near absolute zero, these atoms can still have different nuclear spins. Strangest of all, information about nuclear-spin states of the Sr atoms is able to travel between atoms even when they are super cold. In fact, Fellow Jun Ye’s group, working with theorist Ana Maria Rey’s group, has already measured this inter atom communication in the lab!
Alice realized that if she weren’t trapped in a Sr-lattice optical atomic pocket watch inside a rabbit hole, she could visit JILA and see for herself how the Rey and Ye groups have transformed a Sr-lattice atomic clock into a quantum simulator. Researchers plan to use their precision measurement skills to study quantum magnetism in the simulator, and they have the necessary ingredients to do so.
Such measurements should be possible because spin orientations produce tiny magnetic fields, which can be detected with ultra sensitive precision measurement. However, each spin has a little uncertainty about whether it’s up or down (or some other flavor). This quantum uncertainty can trigger changes in the spins of other atoms, but how this works is pretty complicated.
For one thing, having 10 flavors of nuclear spins in Sr atom nuclei is like having 10 arrows that can point in any direction they want. To make matters even more complicated, the spins can not only communicate with each other, but also switch around and become entangled. When atoms are entangled, when something happens to one of them, the others respond. “Mmm,” thought Alice, “Maybe I could use entanglement to find my way out of this pocket watch.”
Alice looked around to see if she could spot a pathway of entangled pairs of atoms with identical nuclear spin states. Perhaps she could get correlated with them and hop from one correlated pair to another while they were circling around each other until she reached the edge of the watch. It was worth a try, since she could hear her mother calling her from the manor lawn.
Because the pairs of Sr atoms were intimately responsive to one another and to their entangled partners, they thought Alice was just another entangled Sr atom as she skipped across the Fermi sea to the edge of the pocket watch just in time to hop out when the white rabbit checked the time.
Alice jumped to the ground and raced back up the rabbit hole to find her mother. “Mother, there’s a second quantum revolution happening at JILA,” she exclaimed. “Scientists in the Ye and Rey groups are working on understanding and controlling every single quantum state of all 1000 Sr atoms in a single atomic clock.”
“They’re going to solve the mystery of superconductivity and make quantum computers. They are going to figure out how colossal magneto resistance works, all because they can control everything inside this really cool quantum simulator!”
“Yes, of course, dear. Now wipe the sleep out of your eyes and freshen up for dinner,” Mother said.