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Quantum Physics Division
INTRODUCTION
The Quantum Physics Division (QPD) and JILA—the latter established in 1962 and located on the campus of the University of Colorado, Boulder (CU)—together comprise a very unusual but extremely successful collaboration involving the NIST Physical Measurement Laboratory and CU. In fiscal year 2017, JILA received 31 percent of its funding for research and training from CU, 32 percent from NIST, and 38 percent from other federal agencies.1 An important aspect of JILA funding is the JILA Physics Frontier Center (JILA PFC). The first National Science Foundation (NSF) PFC grant to JILA covered the 5-year period from mid-2006 through mid-2011. The award was $3.2 million per year. The NSF PFC 5-year renewals since that time have remained at $3.2 million per year, including the most recent renewal to begin in mid-2018 through mid-2023. There has never been a lapse in group grant or PFC funding since that funding began.
JILA has 10 NIST-supported fellows, the chair of JILA among them, out of a total of 28 JILA fellows. The JILA fellows act effectively as a faculty department at NIST/CU. They collectively and remarkably coherently make hiring decisions and try to guide JILA toward new frontiers in quantum physics and biological physics, among other areas. The presence of biological physics NIST JILA fellows is another example of how JILA marches somewhat to its own drumbeat as to the future of quantum physics very broadly defined.
ASSESSMENT OF TECHNICAL PROGRAMS
The NIST QPD/JILA effort is clearly among the best in the world. Two of the fellows have been among the Reuter’s top 100 most-cited physicists2 for the past 5 years. The Cornell group is both overseeing the first Bose-Einstein Condensate (BEC) experiment in microgravity at the International Space Station (ISS) and testing fundamental high-energy physics with work to set limits on the electron electric dipole moment. The Rey Theory Group is driving a spectacular theoretical effort to understand quantum many-body effects in cold atom three-dimensional (3D) lattices, central to the remarkable10−19 stability limits in the Ye Group’s lattice clocks.
The death of Deborah Jin in September 2016 was a tragic loss. Her work on fermion cold atom lattices was central to the Ye Group’s work. Because her group was extremely well embedded in many JILA projects and central to them, her group was seamlessly absorbed into other groups and what could have been a really major technology blow was averted.
QPD/JILA has strong overlapping interests with other PML divisions, in particular the Time and Frequency Division (TFD). Because QPD/JILA is housed in a CU facility and not at NIST Boulder, there is little trickle down of improvements in the TFD to QPD/JILA.
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1 Tom O’Brian, “JILA: NIST/CU Partnership for Research, Innovation and Training,” presentation to the committee, May 1, 2018.
2 Further information, see Clarivate Analytics, “2017 Highly Cited Researchers,” https://clarivate.com/hcr/2017-researchers-list/#categories%3Dphysics, accessed September 27, 2018.
It would be worth exploring the possibility of stronger technical coordination between the TFD and QPD/JILA to avoid barriers to cooperation (e.g., “not invented here”) within the divisions, given the overlapping agendas. CU, the partner with NIST in JILA, funds only a small portion of its total budget from state appropriations and depends ever more heavily on increases in tuition charges. Maintaining JILA facilities and paying the salaries needed to attract the best people could become extremely difficult as costs rise and federal budgets are less assured. With respect to the latter, the group relies on NSF to fund its PFC and must apply for renewed funding every 5 years.
Quantum Physics
Much of the current research carried out by the Ye Group, the Rey Theory Group, and the Bohn Group exploits the remarkable control achieved in the preparation and observation of ultra-cold atoms trapped in optical lattices to produce revolutionary advances in metrology, in many-body physics, and fundamental physics.
A substantial part of this work finds its original motivation in the desire to build atomic clocks of increasing precision, with a current state of the art of about 1 part in 1019. Understanding what limits this precision and degrades the performance of such atomic clocks relies on a detailed study of many-body effects in atomic and molecular systems. This, in turn, has led to the realization that these many-body effects, which can be under exquisite experimental control in clock development, permit the investigator to simulate experimentally, and study theoretically, a number of challenging problems at the interface between atomic, molecular, and optical (AMO) physics and condensed matter physics. As a result, in addition to their metrological applications, lattice clocks can now be used as quantum simulators of complex interacting, open driven quantum systems whose understanding remains a considerable challenge. In a sense, the research in the Quantum Physics Group can be understood as exploring quantum physics with highly accurate clocks.
Examples of such problems tackled by the Rey Theory Group and its collaborators include, but are not limited to, quantum magnetism, the study of AMO analogs of systems where localized magnetic moments interact with one another or with mobile fermions, such as AMO analogs of the SU(N) lattice models;3 quantum systems and quantum engineering, the investigation of the behavior of open driven and interacting many-body systems, one of the frontiers of modern quantum physics; and cold molecule physics, a topic driven by and feeding into the experimental capability developed in the Ye Group to control experimentally the initial state of molecules, monitor how they approach each other and their intermediate states, and analyze the end products in a situation where the molecular reaction processes are essentially limited only by the laws of quantum mechanics.
The experimental side, led by the Ye Group as well, implements this broad vision, together with the fusion of quantum many-body physics and metrology, which results in world-leading research of the highest quality and interest. Noteworthy here is the work on the optical lattice clock, currently having a precision of approximately 10−19, with the further promise to reach 10−21 in the coming years, owing to developments of a fermionic atomic lattice clock. There seems to be no apparent fundamental limit to how good this system can become, and at this point, the fusion of metrology and many-body physics should be expected to be further enlarged, opening up fascinating new directions of research in both applied and fundamental physics. The latter might include use of such clocks for gravitational wave detection, searches for dark matter, long baseline interferometry, geodesy, searches for physics beyond the Standard Model, and more. Much as the development of clocks has historically been at the center of discovery and scientific breakthroughs, and so too the quest for ever-increasing precision will continue to open up unexpected avenues of inquiry.
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3 See, for example, M.E. Beverland, G. Alagic, A.P. Koller, A.M. Rey, and A.V. Gorshkov, 2016, “Realizing exactly solvable SU(N) magnets with thermal atoms, Phys. Rev. A 93(5):051601(R).
The Thompson Laboratory has extended the discussion of precision measurements with single quantum objects to new possibilities with many quantum objects. One important application is reducing quantum noise by entangling, for example, spin states. This has already enabled surpassing the standard quantum limit by 17.7 decibels (dB). The group also described realizing an idea of the noted physicist Robert H. Dicke—a superradiant laser that is insensitive to fluctuations in the cavity length because the bandwidth of the emission is much smaller than that of the cavity resonance frequency.4 This results in a laser 500,000-times less sensitive to cavity length than conventional stable lasers.
The exceedingly narrow linewidth of the superradiant laser can be further improved by utilizing forbidden transitions with even longer lifetimes (i.e., with narrower linewidths). The potential exists for orders of magnitude improvement, which can lead to improved clocks and applications in fundamental science, such as general relativity. The approximately 60-fold improvement over the standard quantum limit obtained by squeezing via entanglement can be further improved, opening up applications to optical lattice clocks and matter wave interferometers.
The research plan of the Kaufman Group is to marry the tools of quantum gas microscopy, optical tweezer technology, and high-precision spectroscopy in order to gain single-particle control at fundamental length scales and very small energy scales. The work of this group is expected to continue to impress.
The work of the Cornell Group has carved out a unique space in the world of BEC, and their work with the electron electric dipole moment (EDM)—work that is already challenging some of the more conventional improvements to the Standard Model—is among the best in the world. The purpose of this experiment is to make a precision measurement of the EDM of the electron. Because a finite electron EDM violates time symmetry, and thus by the CPT5 theorem violates CP symmetry as well, a precision upper bound on an electron EDM constrains the Standard Model. Cornell also works in collaboration with the Ye Group6 using an ultracold gas of Rubidium-85 to create a strongly interacting BEC, which will provide an ideal platform to study few- and many-body physics.
The Lehnert Laboratory works on a number of different topics, including the transduction of mechanical motion into electrical signals; development of Josephson parametric amplifiers from an arcane and poorly understood device to what is now a heavily used, quantum-limited amplifier central to superconducting qubit development; and, more recently, development of an optomechanical transducer connecting microwave and optical signals. Prior to starting this last effort, the group had led the first effort to successfully use light to cool a mechanical resonator to its quantum ground state, adapting the AMO technique of sideband cooling and applying it to a microwave system to achieve this result.7 The group’s parametric amplifiers are being used in a collaborative effort involving Yale University, the University of California, Berkeley, and Lawrence Livermore National Laboratory to search for axions,8 which, if detected, would have very important implications for fundamental physics and searches for dark matter.
The optomechanical transduction effort is in a highly competitive area, with perhaps a dozen quite different but similarly targeted efforts worldwide. This effort is being pursued, in what seems a signature of JILA, as a close collaboration with the Regal Laboratory of JILA. This JILA collaboration has achieved more benchmark advances than any of the competing efforts. The most recent demonstration includes the highest-efficiency (by a couple of orders of magnitude) bi-directional transduction of coherent signals between the optical and microwave frequency domains. While not yet operating in the
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4 James Thompson, JILA, “Quantum many-body states for precision measurement,” presentation to the committee, May 1, 2018.
5 CPT = charge conjugation (C), parity transformation (P), and time reversal (T).
6 Further information available at JILA, “About the Ye Group,” http://jilawww.colorado.edu/ye/, accessed September 27, 2018.
7 Konrad Lehnert, JILA, “Quantum transduction between the microwave and optical domains,” presentation to the committee, May 2, 2018.
8 The axion was postulated to account for strong charge-parity symmetry in the Standard Model.
quantum limit, this experiment is close to doing so, with no obvious roadblocks other than improving the performance of each element involved in the transduction.
This technology could prove central to building practical quantum communication networks and comprises a very remarkable advance. Note that the devices involved in this are highly sophisticated combinations of a superconducting, extremely low-loss, microwave resonator; a very high finesse optical cavity; and a carefully designed, high-quality-factor silicon nitride membrane with superconducting metal patterned on its surface, through which the optical and microwave signals are coupled to one another. The successful fabrication of these devices uses the PML cleanroom9 quite heavily, and the use of these devices employs very sophisticated microwave techniques (relying on the Lehnert Laboratory’s expertise) combined with optical techniques (relying on the Regal Group expertise) in a way that would be hard to reproduce anywhere but at JILA.
The Nesbitt Laboratory performs experiments in the areas of biophysics, nanoscience, chemical physics, and molecular spectroscopy. One nanoscience project focuses on the fundamental nature of the quantum confined exciton state, and luminescence blinking, in single core/shell chemical quantum dots via their response to very high electric fields. This is a central problem in semiconductor quantum dots, and despite intensive worldwide effort remains poorly understood. A second project explores femtosecond (fs) hot electron relaxation dynamics and photoemission in single plasmonic gold (Au) nanostructures of various shapes. Here the laboratory has made the remarkable discovery that the direction of photo-emitted electrons is often at right angles to the optically excited plasmon axis. This points to unexpectedly complex relaxation kinetics during the 30-fs relaxation process. This discovery is an important step in helping to understand the recently discovered ability of hot electrons in optically excited Au nanostructures to catalyze surface chemical reactions.
Accomplishments
The division’s optical lattice clocks have a precision of approximately 10−19, with the further promise to reach 10−21, owing to development of a fermionic atomic lattice clock. A further novelty is the realization of Robert H. Dicke’s idea of a superradiant laser that is insensitive to fluctuations in the cavity length owing to its emissions bandwidth being much smaller than that of the cavity resonance frequency. The result is a laser 500,000 times less sensitive to cavity length than conventional stable lasers.
Opportunities and Challenges
QPD/JILA has strong overlapping interests with other PML divisions, in particular the Time and Frequency Division. Because QPD/JILA is housed in a University of Colorado, Boulder (CU) facility and not at NIST Boulder, there is little trickle down of improvements in the Time and Frequency Division to QPD/JILA.
Biological Physics
In biophysics, the Nesbitt Laboratory studies the effects of molecular crowding such as occur in live cells on the kinetics and thermodynamics of biochemical processes, including ribonucleic acid (RNA) folding. Under crowded conditions, single-RNA molecules folded 35-times faster than in the dilute solution. Crowding also led to a modest decrease in the unfolding rate. In related work, the folding–unfolding kinetics of a ubiquitous tertiary interaction motif, the GAAA10 tetraloop–tetraloop receptor
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9 The clean room is part of the Quantum Electromagnetics Division of the Physical Measurement Laboratory.
10 G = guanine; A = adenine.
(TL–TLR), was investigated by single-molecule fluorescence resonance energy transfer spectroscopy in the presence of natural amino acids both with (e.g., lysine, arginine) and without (e.g., glycine).11 This is a productive line of research relevant to cellular chemical biology.
Impressive advances were made in the time resolution and noise characteristics of biological atomic force microscopy (AFM) for membrane protein studies at the Perkin’s Laboratory.12 By shaping the cantilever, by focused ionic beam (FIB) machining, and by optical stabilization of both sample and tip, remarkable combinations of time resolution (~ 1 microsecond) and low noise were achieved. This very substantial advancement was applied to the unfolding dynamics of bacteriorhodopsin in near native purple membranes. The experiments are now sensitive enough to reveal multiple unfolding intermediates and reveal the stabilizing effect of binding retinal and of individual amino acids.
The work of the Jimenez Laboratory combines ultrafast laser spectroscopy with microfluidic development in biological physics. The group is working on developing microfluidics-based single-cell spectroscopy techniques to characterize photophysics in vivo on 105-member libraries of fluorescent proteins. This laboratory uses microfluidics to isolate fluorescent protein clones with new properties and discover structure-dynamics relationships that would not be apparent from conventional biophysical studies focusing on a small number of variants.13
The Jimenez Laboratory also is conducting a new effort exploring the unique properties of entangled photons interacting with fluorescent proteins and other fluorophores used in cellular imaging. Time-energy entanglement can significantly enhance nonlinear light-matter interactions. Entangled two-photon absorption follows linear rather than the classical quadratic intensity dependence and can be observed at much lower photon fluxes than two-photon absorption in conventional multiphoton microscope.
Accomplishments
The use of single-molecule fluorescence resonance energy transfer spectroscopy in the presence of natural amino acids, both with (e.g., lysine, arginine) and without (e.g., glycine), is a productive line of research relevant to cellular chemical biology. The use of biological atomic force microscopy (AFM) for membrane protein studies achieved time resolution (~ 1 microsecond) and low noise.
Opportunities and Challenges
The efforts in biological physics are strong, but at a subcritical mass, with the compounding circumstance that the two biophysicists are somewhat isolated, making it a challenge to ensure their work is relevant. The Biology Frontier Center on the CU campus may be an important resource. PML could provide an environment in which JILA scientists working in biophysics continue to work on problems of priority to both biologists and biophysicists. This could include fostering collaborations and other mechanisms that bring them closer to the Biology Frontier Center as well as other options.
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11 A. Sengupta, H.-L. Sung, and D.J. Nesbitt, 2016, Amino acid specific effects on RNA tertiary interactions: Single-molecule kinetic and thermodynamic studies, J. Phys. Chem. B. 120(41):10615-10627.
12 Thomas Perkins, JILA, “Improved bioAFM for probing diverse molecular systems,” presentation to the committee, May 1, 2018.
13 Adapted from JILA, “The Jimenez Lab: About Ralph Jimenez,” http://jila.colorado.edu/jimenez/node?page=2, accessed October 1, 2018.
PORTFOLIO OF SCIENTIFIC EXPERTISE
The program’s scientific expertise is closely matched to the technical programs and strongly enables QPD/JILA’s ability to be a world leader in quantum physics.
ADEQUACY OF FACILITIES, EQUIPMENT, AND HUMAN RESOURCES
The facilities at QPD/JILA are unique and the envy of many physics departments around the world, who have seen the steady erosion of facilities, in particular in human resources, in the shortsighted interests of local budget issues. QPD/JILA maintains a strong electronics shop where students work with staff to build things, an excellent machine shop both at the professional level and for students, and a fantastic glass shop. It is extremely important that this range of facilities and support staff remain.
Challenges and Opportunities: Facilities
However, there are some black clouds on the horizon. The JILA Laboratory is a mix of old and new construction, with the oldest part of the laboratories being simply incompatible with the extraordinary experiments being pursued there, and the newer parts of the laboratories not having been built to the highest level of temperature and humidity control. In spite of this, the control of vibration in the basement is at world-class level.
A complete renovation of the oldest wing of the laboratory, at the least, needs to be funded jointly by NIST and CU and completed in a timely fashion, in order that the world-class researchers have the best vibrational-, temperature-, and humidity-controlled laboratory space.
DISSEMINATION OF OUTPUTS
Outreach
JILA participates in the CU Wizards program, which explores the exciting worlds of physics, chemistry, biology, geology, mathematics, psychology, astronomy, and more. It is free to the public and geared toward children in grades K-12 and their families.
The CU Physics Department offers several 1-hour talks on Saturday afternoons. These afford adults and high school students the opportunity to interact with a CU professor, including JILA fellows. A further program, called Alice’s Adventures in Quantumland incorporates JILA research on the novelties of quantum physics. It is in a whimsical narrative form, aimed at introducing a younger audience to the concepts of quantum physics.
JILA embraces the goal of providing “a supportive and welcoming environment for women scientists of all ages.”14 However, while JILA has some high-profile women and minority researchers, as well as a number of female postdoctoral researchers and graduate students, efforts to further recruit and advance both groups need to be continued.
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14 University of Colorado, Boulder, “Outreach,” http://amalfi.colorado.edu/resources/outreach, accessed October 1, 2018.
Stakeholder Needs
It is difficult to assess to what degree the work of the division is driven by stakeholder needs. By its very title, the QPD has a strong emphasis on fundamental quantum physics. Remarkably QPD/JILA has now moved into the realm of testing fundamental aspects of general relativity and physics beyond the Standard Model of high-energy physics. In that sense, the stakeholders of the QPD/JILA effort are the community of fundamental scientists.
Owing to the unique charter of JILA among NIST laboratories, consideration is given to the educational stakeholders of QPD/JILA by recruiting and training the next generation of top students and postdoctoral researchers. QPD/JILA does a remarkable job for the educational stakeholders, which is a beneficial arrangement for CU. It might be instructive to see an accounting of the numbers of students and postdoctoral researchers passing through JILA in the past 5 years, together with categorization of where these people are now (industry, national laboratory, academia, entrepreneurs, and so forth).
Another interesting area with respect to stakeholders is biological physics. Here the Jimenez Laboratory, Perkins Laboratory, and Nesbitt Laboratory perform valuable functions. The Jimenez Laboratory is deeply involved in doing directed evolution of fluorescent protein biomarkers using advanced laser technology and microfluidics, and it recently has a very challenging but exciting project to use entangled 2-photon excitation to dramatically increase 2-photon cross-sections for use in biomedical tissue imaging. The Perkins Laboratory has made dramatic improvements in AFM cantilever technology to achieve microsecond response times in AFM microscopes, which will have immediate and important use in the rapidly expanding AFM imaging world, both for materials sciences and biology. The Nesbitt Laboratory is expanding fluorescence resonance energy transfer (FRET) imaging microscope technology, which plays an important role in many aspects of protein dynamics, and the work on electron emission from nanoscale objects could have important implications for electron gun development used in many technology areas.
Opportunities and Challenges
Technology Transfer
The challenges are complex. While JILA is mostly engaged in basic scientific research not compatible with patent protection and licensing, protecting some of the work would allow it to be translated into the commercial sector. Without intellectual property (IP) protection, companies will not want to invest the time and money to complete translation to market. Incentives for JILA researchers could be constructed that reward IP development, compatible with government restrictions, in a manner that does not distort the basic scientific effort but promotes technology transfer. Currently, it appears that IP protection and technology transfer are not seen as priorities and are not part of the reward structure, and therefore there is minimal effort to seek patents and transfer valuable technology.
Funding Sources
One concern regarding sources of funding is the degree to which JILA relies financially on its Physics Frontier Center, recently renewed for another 5-year term. There is need for planning how to handle the possible funding downturn should this center not be renewed in the future.
JILA’s plans to hire an embedded fund raiser whose mission will be to raise funds for JILA from philanthropists is sensible.
