Gabriel Patenotte ’21

The Walsworth Group, Harvard University Department of Physics, Cambridge, MA

During the summer, I was fortunate to have the opportunity to do research for Professor Walsworth at Harvard University. The Walsworth Group investigates topics in applied physics where high precision spectroscopy enables the discovery of new science. In recent years, the study of Nitrogen Vacancy (NV) centers in diamonds has overtaken the group’s research. NVs have wonderful quantum properties that were discovered in the late two-thousands. A large portion of them contain a valence electron whose spin can be measured and controlled at room temperature. The spin of these valence electrons is susceptible to external forces, allowing us to use NV-centers as quantum sensors. By measuring how the spin population change across an ensemble of NV-centers in four crystalline directions, we determine a vector field from the forces acting upon each NV. After some calculations, we can reconstruct the source of the field, be it magnetic, electric, or strain within the diamond. A further benefit is that NV centers may be preferentially grown in the top ten nanometers of a diamond. Any sample may then be put on the diamond surface in extremely close contact with the sensors. Through this proximity, NVs achieve remarkable magnetic sensitivity at room temperature. Applications of NVs include high sensitivity NMR spectroscopy, measuring the electric fields of firing neurons, and the detection of WIMP type dark matter.

My project this summer was related NV-NMR. Both traditional NMR and NV-NMR measure the procession of atoms around a bias magnetic field to identify the structure of unknown chemical samples. Yet while traditional NMR requires milliliters of sample and strong magnetic fields to obtain a good signal to noise ratio, NV-NMR needs just picolitres of sample and less than a hundred Gauss for comparable resolution. This high sensitivity will soon allow for the unprecedented spectroscopy of single cells and could make NMR instruments both cheaper and more portable.

My goal, though ambitious, was the implementation of a fluid delivery mechanism that delivers precise quantities of fluid in an automated manner onto the diamond. Up until now, experimenters pipetted drops of sample onto their diamonds. This technique had drawbacks; drop placement was inexact, the diamond surface could become easily contaminated with a prior sample, and debris from the environment could fall into the liquid. To solve this, my mentors suggested that I use microfluidics—a technique that involves patterning a substance with micron wide channels. Such channels operate at a length scale where laminar flow dominates. As a result, microfluidic systems can transfer fluids with precision and speed and avoid mixing between layers. For NV applications, this translates to fast sample delivery with the guarantee of no contamination.

I came in knowing nothing about NVs, microfluidics, or quantum mechanics, which meant that I had a steep learning curve. I read prior theses, attended colloquia on NV centers, and observed my colleagues in the cleanroom as they carried out procedures. My first chips had leakage problems; I would push the fluid into the inlet port only to see it come out of the interface between the channel substrate and the diamond. Eventually I redesigned my channels and changed the chemical concentrations within the glue, which produced a chip that was leak-free, robust, and easy to make. I had, however, ignored the microwave loop, which was difficult to integrate within the device. For about I month I tried all sorts of ideas; placing a 50-um wire within a channel, weaving a wire into a spiral, creating an incision that would hold the wire, and melting solder inside a channel that would wick itself along the entirety of any complex pathway. Yet the wire was smaller than a human hair and quite challenging to shape, and the solder melted when I applied the necessary 16 watts of power. These were merely setbacks, however, as I eventually designed a resonator that would deliver a strong magnetic field to control the NV spin-state.

My time at the Walsworth Group was transformative, in the most positive sense of the word. I was serious about physics before I left for Cambridge, but I did not know what being a graduate student entailed. I worried about dedicating seven years of my life to a project, and I had no idea what I would do after those years were over. In the Walsworth Group, I found a welcoming environment with all sorts of answers. My colleagues were role models; kind, motivated scientists that had the highest of dreams but that were extremely collaborative. They treated me well, and they approached me as though I were a graduate student. Since microfluidics was a new technique in the group, I quickly become an “expert” at the technique. At meetings I would play a central role in the conversation, and I occasionally suggested ideas that they had not thought of before. This mock-graduate experience was terrific; I enjoyed controlling my own project and the freedom of working twelve hours a day in whatever way that I preferred. In fact, I enjoyed the graduate lifestyle so much that I chose to extend my project by two weeks. While there is still much that I do not know about graduate life—what it is like at other institutions or in different groups—I’m excited to go to graduate school and motivated to work hard to follow the steps of my colleagues.

This summer was impactful in so many other ways. In the near term, Professor Walsworth has invited me to present a poster at a laser physics conference in September. I am also a co-author on an upcoming NV-NMR paper that utilizes my device. I mastered many technical skills that will make me a better researcher. I also dabbled in quantum mechanics due to weekly group seminars and optional reading. Lastly, I learned a lot about myself, and I feel much more capable and independent than ever before.

I would like to express my tremendous appreciation to the Wong Family for enabling such a terrific summer. Without your generosity, I would not have been able to partake in this superb research experience. Now that my internship is over, I look forward to sharing what I have learned with my peers at Williams in the hope that they too will also have a wonderful summer experience. Thank you.