Lab News

Going up?

Today Xin, Jack, Brett, and Haoran achieved a major milestone in the development of a multiplexed optical lattice clock and its use for new tests of relativity. The animated GIF below shows strontium atoms in an “atomic elevator” made of light, rising with respect to gravity (which is pointing down in this image) at a rate of ~3 mm/second.

The second image below, also taken today shows the preparation and simultaneous imaging of two ensembles of strontium atoms in our vacuum chamber, spatially separated by ~1 mm, a critical component of our new “multiplexed optical lattice clock” design.

This is a major step towards measuring the “gravitational redshift” due to earth’s gravity at a new length scale. In a gravitational field such as Earth’s, a clock that is elevated with respect to gravity will tick faster than a lower clock. This effect of general relativity is called the gravitational redshift, and it has previously been observed at the ~30 cm scale, but has not yet been observed at the cm or mm scale.

As shown in A in the diagram below, the Einstein equivalence principle, a foundational tenet of the theory of relativity, states that an observer cannot distinguish between being inside an elevator on the surface of earth and experiencing an acceleration due to gravity g (panel I), and being in an elevator accelerating through space with an acceleration a=g (panel II)As shown in B, by combining our multiplexed optical lattice clock with the ability to accelerate atoms as in the “atomic elevator” shown above, we will be able perform a novel and direct test of the Einstein equivalence principle in our lab.

Strontium atoms trapped in a crystal of light

Xin, Jack, Haoran, and Brett have successfully trapped strontium atoms in an optical lattice for the first time! (The first time in our lab, this is already a very well established technique in experimental atomic physics.) The strontium atoms are held in a standing wave of light formed by two counter-propagating laser beams, which forms a simple one-dimensional crystal of light. Below is a picture taken with a CCD camera of the shadow cast by these atoms on a laser beam.

This is a major milestone on the way to building a working optical lattice atomic clock.

Aedan and Matt’s paper published in Physical Review Applied!

Congratulations to Aedan and Matt, whose paper “Fast relaxation on qutrit transitions of nitrogen-vacancy centers in nanodiamonds” has now been published online in Physical Review Applied! For those who don’t have access to the journal, a pre-print can be found on the arXiv here:

And if you prefer to get your physics fix in doses of 140 characters or less, here’s a tweet from the department communications director Sarah Perdue summarizing our paper (based off a much longer synopsis provided by Shimon):

Kolkowitz lab becomes the coldest place in Wisconsin!

As mentioned in a previous post, for the past few months the cloud of atoms in the center of the strontium optical lattice clock vacuum chamber in the Kolkowitz lab has held the (somewhat dubious) honor of being the second coldest place in Wisconsin at a temperature of ~1-2 milliKelvin, with the Saffman lab down the hall beating us out by a factor of ~1000x or so with their cesium quantum computing experiment, which reaches temperatures of ~2-5 microKelvin. We’re pleased to report that with the implementation of a second stage of narrow-line laser cooling we are now measuring strontium atom temperatures of ~4 microKelvin, making one small 0.5 x 0.5 x 0.5 mm3 volume in our lab the coldest place in Wisconsin (in a two-way tie with the Saffman lab), and one of the coldest places in the known universe.

The camera images above are “time of flight” images of a cloud of ~1 million strontium atoms after we have released them from our narrow-line magneto-optical trap. (The images are actually the shadows cast by the atoms on a laser beam, which is a common atom imaging technique called “absorption imaging.”)  After they are released the atoms fall due to gravity and spread out due to their finite temperature, with the rate of expansion of the cloud providing an easy measurement of their temperature. Here, the average speed of the atoms is ~ 0.02 meters per second, or ~ 0.04 MPH, corresponding to a temperature of ~4 microKelvin. This is roughly the speed of a garden snail. For comparison, nitrogen molecules in air at room temperature have an average speed of about ~500 meters per second, or 1000 MPH.

Shimon’s “quantum seal” paper with Shelby Kimmel published in Physical Review A!

Shimon’s paper with co-author Professor Shelby Kimmel of Middlebury College, “No-go bounds for quantum seals,” was published online in Physical Review A today. The paper is a theoretical analysis of the feasibility of “quantum seals.” And in case you’re wondering, no, this isn’t just an aquatic version of Schrödinger’s cat… The kind of seals we’re talking about here are the quantum version of the wax seals used to secure letters and packages, not the seals that bark and eat sardines.

No, not this kind of seal… Image credit: Ellen Cuylaerts/HotSpot Media, courtesy of the Daily Mail.

In our paper we analyze whether it’s possible to use quantum mechanics to encode a message such that the receiver of the message can read it without additional communications with the sender, but the sender can tell whether or not the receiver (or someone else) has read the message and broken the “quantum seal.” While this at first might seem doable because of the disturbances measurements tend to create in quantum mechanics, we build on previous work to prove that it is sadly impossible to make a quantum seal that both gives the receiver of the message a high probability of successfully reading it, and the sender a high probability of telling if the seal has been broken or not.