Richard Packard with a lab member
Richard Packard, Professor of Physics at UC Berkeley, passed away in November 2024 after a brief illness diagnosed only a month before. He was 81. Richard grew up in Buffalo, New York. In high school he displayed his aptitude for building things by constructing a 16’ sailboat and successfully launching it. He remained an avid boater, sailing and racing in the San Francisco Bay, and for many years spent entire summers in Alaska on a 30’ fishing boat.
His Ph.D. was with T. M. Sanders at the University of Michigan, studying the onset of vortex lines in rotating superfluid 4He at 1.2 Kelvin (degrees above absolute zero). Richard Feynman had predicted in the 1950’s that a rotating bucket of superfluid would be filled with an array of quantized vortex lines, with the number of lines proportional to the rotation speed. By trapping electrons on the vortices and then measuring the total charge, Packard and Sanders were able to observe jumps in the collected charge as the rotation slowly increased, confirming the entrance of vortices.
After two years as a postdoc at Berkeley with Fred Reif, Richard became an Assistant Professor, and set out to build a much larger rotating cryostat that could get to lower temperatures, below 0.1 Kelvin. At that temperature there is little vapor above the liquid helium, and the electrons coming from the vortex cores could be accelerated into a phosphor screen, giving a dot of light that marked the position of each vortex. Initial photographs were able to successfully image the vortex positions, and later on a TV camera on the rotating cryostat was able to study the motion and oscillations of the vortex array in great detail. A congratulatory letter from Feynman noted his “great pleasure for me to see your photographs. Visions in the head at night twenty years ago coming out in black and white physical reality”.
Richard then turned to studies of superfluid 3He, which had just been discovered at Cornell. This required temperatures below 0.003 Kelvin, since 3He is a fermion, and it was thought the quantum condensation into a superfluid could only occur when two 3He atoms form a bound pair, effectively becoming a boson. Richard built a copper demagnetization cryostat to get to those temperatures, and his first experiments were to study the flow of the 3He through small orifices, measuring the critical velocities where the superfluid flow breaks down. He then built a rotating cryostat to study the unusual properties of vortices in the superfluid 3He, collaborating with a Japanese group in this. A major result in the rotating cryostat was a measurement of the quantum of circulation characterizing the flow pattern of a vortex. In 4He this was known to be Planck’s constant divided by the mass of a 4He atom, but Richard showed in superfluid 3He that the result was Planck’s constant divided by two 3He atomic masses, confirming definitively that the 3He atoms form a bound pair to condense into the superfluid state.
Richard Packard at UC Berkeley
Another major result was Richard’s discovery of Josephson oscillations in both superfluid 3He and 4He. Brian Josephson’s Nobel Prize-winning prediction of oscillating microwave currents between two superconductors coupled by a weak link had long been studied in superconductors, but had not been observed in superfluids. Richard used nanotechnology to form a weak link consisting of thousands of tiny micron-sized holes in an atomically thin silicon membrane, which was mounted between two chambers filled with superfluid 3He. A pressure difference was applied between the two chambers, causing Josephson currents at acoustical frequencies to flow at amplitudes that could easily be heard with headphones in the lab. This was a distinctive “whistle" whose frequency decreased as the pressure decreased across the two chambers, in exact agreement with Josephson’s prediction. Josephson effects were also discovered in 3He nearly simultaneously by a French group, but with much smaller amplitude since they used only a single orifice for the flow. Both groups realized that the Josephson currents would be very sensitive to rotation of the cryostat, and both were quickly able to measure the effect of the Earth’s rotation on their stationary cryostats. In later years Richard discovered that similar Josephson oscillations could be observed in superfluid 4He at temperatures very close to 2.176 Kelvin where the helium transforms to the normal state. This allowed him to form quantum interference devices using the Josephson junctions with very large effective areas, making them extremely sensitive to flow and to rotation, even approaching the sensitivities of the best ring-laser gyroscopes. His work in this area was immortalized in the television series The Big Bang Theory. The “scientists” in that show invent a “superfluid helium gyroscope” that they think will make them millions, only to have it stolen from them by the Army in the last episode.
For his outstanding research accomplishments, Richard was awarded the Fritz London Memorial Prize in 2005, the most prestigious international prize in low temperature physics. Richard was also an exceptional teacher, winning the 1990 Donald Sterling Noyce Prize for Excellence in Undergraduate Teaching. He would often invite the students in his classes (even the ones with hundreds of students) to his home for food, conversation, and a little guitar playing.
A friend and neighbor of Richard's, John Cummins, summed up his nature with a tribute:
"Richard‘s problem solving abilities, his humbleness and his generosity extended to his private life as well. His carpentry, plumbing and electrical skills were always available to his neighbours at any time of the day or night, as was his large collection of tools. More recently, as empty nesters, he and his wife Roseanne made room available in their home for two young Afghan women refugees for more than two years at no cost. As an avid sailor and adventurer throughout the world, he routinely brought many of his friends along as guests, particularly on his sojourns in Alaska."
Richard was a professor at UC Berkeley for 37 years, from 1971 until 2008. He is survived by his wife Roseanne, sons Ben and Daniel, daughter Suzanne Swift, and grandchildren Jacob, Lily, Tallula, and Elijah.