2 Apr 2021 by amj

It was an honor to represent our group and present our work for the Virtual Atomic, Molecular, and Optical physics Seminar series (VAMOS). The talk, "Radium ions and cold radioactive molecules", was recorded and can be conveniently watched on YouTube. I discuss our recent radium ion measurements, our progress with radium-based molecules, and some of the motivations for our research, as well as our plans moving forward. The post talk discussion (not recorded) with students, postdocs, and a few P.I.s was a highlight - lots of fun ideas were explored! Thank you to the VAMOS organizers for giving me this opportunity.

The work by Nick Hutzler and Phelan Yu on RaOCH3+ (radium monomethoxide) and its potential to address the mystery of the Universe's matter-antimatter asymmetry was featured in an article on phys.org.

11 Mar 2021 by amj

Graduate student Mingyu Fan gave a seminar to CERN's ISOLDE Physics Group. ISOLDE has made seminal measurements on radioactive molecules, in particular RaF. They were happy to hear about Mingyu's recent paper where we demonstated the controlled production of cold, trapped radioactive molecules.

Our work on the controlled synthesis and detection of radioactive molecules was published today in Physical Review Letters. In the paper we demonstrate a new all-optical technique for identifying trapped ions by their mass in an ion trap. The technique, optical mass spectrometry, has several advantages: it is non-destructive and fast. We applied the technique to detect the synthesis of radioactive molecules that are exceptional sensors for addressing open questions related to time symmetry violation.

The paper was the culmination of an incredible process that started with grad student Mingyu Fan one day noticing that the trapped ions he was working with were excited to large motional states if he changed one of our laser's frequencies by a small amount (~10 MHz). We discussed and I encouraged Mingyu to explore what he had stumbled upon by chance. In short order Mingyu had figured out how to convert a signal from the amplified motion into a mass of the trapped ions. Mingyu then worked out the mechanism behind the motional amplification (see the paper for an explanation). We then decided to apply this new ion identification technique to radioactive molecules, which we were confident we could make, but didn't have a great means to confirm production until this point. Mingyu and Craig produced RaOH+ and RaOCH3+ by reacting trapped radium ions with trace quantities of methanol that was controllably leaked into the vacuum chamber. These molecules are great for addressing a pair of old and pressing problems: first, how is it that there is a massive imbalance between matter, which is abundant, and antimatter, which is practically nonexistent, in the Universe - the Baryon asymmetry problem, and second, why does quantum chromodynamics seemingly preserve charge conjugation and parity symmetry, known as the Strong CP problem.

The figure, by Max our resident artist, is a depiction of optical mass spectrometry where a pair of bright laser-cooled radium ions surround an unknown dark ion. Photons (teal) are detected and converted into a signal (red) that tells us the mass of the unknown ion.

In addition to using optical mass spectrometry with radium and radioactive molecules, a team led by undergraduate Xiaoyang Shi applied the technique to identify the four stable strontium isotopes in the significantly different environment of a high frequency ion trap. It was great to have so many people in the lab and to utilized both of our ion traps for this work. I was also happy that Xiaoyang was able to get data with the trap he built before he graduated - he has since started physics grad school at MIT.

The motivation to produce RaOCH3+ stemmed from a conversation in the fall of 2019 with Nick Hutzler. Later, Nick and graduate student Phelan Yu started working on a paper about this molecule for its potential sensitivity to new physics. It was special to submit our paper jointly with Nick and Phelan's work to PRL, and go through the review process in parallel with them. Our papers were both featured as Editor's Suggestions, and Ronald Garcia Ruiz wrote up a very nice APS Physics Viewpoint article about the letters.

The work was also featured in the UC Santa Barbara Current in an article by Harrison Tasoff - Enlightening Dark Ions.

In the lab we're hard at work on the exciting next steps!

Great news, the lab has now had its first set of UC Santa Barbara undergraduates on a publication that came out today in PRA. The work measured a specific transition in Ra+ to resolve a discrepancy between previous values by means of directly driving the transition in question. Grad student Craig Holliman spearheaded the entire effort, really leading the others scientists on the paper. As an advisor it was great to watch Craig take full ownership of this experiment, organize people to configure the experimental setup, write code for data taking, take the data, and perform the data analysis. Undergrad Michael Straus made critical contributions to the data analysis, and undergrad Asad Contractor was instrumental in setting up the experiment, taking data and helping refine the manuscript that Craig wrote.

The Gordon and Betty Moore Foundation have give me a Fundamental Physics Innovation Lectureship Award to visit Michigan State where I'll be hosted by Jaideep Singh. I'll present on the possibility of using molecular ions, in particular radioactive molecules with heavy octupole deformed nuclei, for searching for new physics beyond the standard model. We'll discuss the possibility of setting up a tabletop ion trapping experiment at the Facility for Rare Isotope Beams which could study rare isotopes and molecules containing such isotopes at high precision.

In collaboration with Amar Vutha and his student, Mohit Verma, we worked on a new proposed permanent electric dipole moment (EDM) measurement technique that was published today in PRL. EDMs are at the forefront of the search for new physics beyond the Standard Model of particle physics to explain several major open issues, including the Universe's lack of antimatter. In the early history of the Universe matter and antimatter were created in nearly equal quantities, recombined and annihilated (this is what happens when matter and antimatter collide), and a bit of matter was left over, ultimately the material that we are made of. The known laws of physics are not enough to explain this excess of matter over antimatter, and thus we need to look to new physics to explain this discrepancy. One of the conditions for this is new physics that violates time symmetry. When time symmetry is broken a system looks fundamentally different if we reverse the arrow of time. Permanent electric dipole moments violate time symmetry, but so far no EDMs have been found. A brief aside: the electric dipole moment of molecules is not a permanent electric dipole moment, it is an electric dipole moment that has been induced by applied electric fields and does not violate time symmetry. Measuring an EDM would be a clear sign of new physics, and has motivated many searches worldwide for them in systems such as neutrons, atoms, and our personal favorite: molecules. Amar had the brilliant idea that we could utilize special molecular states that are insensitive to magnetic field noise, so-called clock states, and that this would extend the reach of EDM searches to wide classes of molecules that can be prepared with exquisite control. In our group we are really excited to apply this technique to single molecular ions that are highly sensitive to new physics, such as RaOCH3+. The technique should be straightforward to implement in an ion trap where we can apply the requisite control voltages (a small voltage due to small size of the ion trap) on the trap's end cap electrodes. For a great talk on the proposed technique watch Amar's talk at FSQT.

In only a couple of years since they realized the first laser cooling of radium ions graduate students Mingyu Fan and Craig Holliman have now cooled radium to its quantum ground state of motion. This is an incredibly exciting starting point for many new research directions with this very heavy atom. Ground state cooled radium means they have essentially full control over the ion, with the ability to very accurately measure the system, or now use phonons, the quantum of motion, to control or readout other co-trapped atoms or molecules. One remarkable aspect of this result is the trap in which the cooling was done: the trap was specifically designed for the first laser cooling and spectroscopy of radium, and the creation of radium molecules, it was in no way designed for cooling to the motional ground state. You can see this in the figure where the motional mode that is cooled is only around 230 kHz where typical ground state cooling happens with motional frequencies around 1 MHz or higher in traps that are much smaller (see our ground state cooling working with the lighter strontium ion). The trap dimenions are r_0 = 3 mm and z_0 = 7.5 mm (the characteristic distances from the radial and axial electrodes to the ion) - this is a very large ion trap by quantum information science standards. The figure shows the probability that the ion can be driven to excited state by light at 728 nm while simultaneously adding or substracting a motional quantum. The small red peak shows that no more phonons can be removed from the system as the average ground state occupancy is 0.12 total phonons. This work was assisted by UC Santa Barbara undergrad Asad Contractor who recently joined the project and is already working on implementing an advanced ground state cooling scheme. With ground state cooled radium Mingyu, Craig, and Asad are actively working on quantum state engineering to further advance the lab's capabilities.