ASSESSMENT OF TECHNICAL PROGRAMS
The Quantum Physics Division (QPD) has a diverse range of programs, including nanotechnology and biological physics, but it continues its firm and unified base in metrology, appropriate for the programs’ association with NIST. New advances in measurement science are at the heart of many major scientific advances, and JILA, the joint institute between NIST and the University of Colorado, Boulder (and, therefore, the Quantum Physics Division), is widely recognized as one of the leading research and training organizations in atomic, molecular, and optical (AMO) physics and closely related areas. JILA has been ranked as the nation’s top AMO graduate program for decades. JILA scientists are responsible for a long list of breakthroughs in AMO physics, such as the world’s first Bose-Einstein condensate, first Fermi condensate, first self-referenced laser frequency comb, first evaporative cooling of molecules, first quantum degenerate gas of polar molecules, and first cooling to the quantum ground state of a macroscopic object (the last-named was accomplished in collaboration with other NIST scientists).
Work on self-referenced femtosecond laser frequency combs was initially pursued as a tool to improve optical frequency standards (atomic clocks), but now laser frequency combs have become one of the most powerful and versatile research and precision metrology tools since the invention of the laser. Laser frequency combs are routinely used across PML laboratories for research and metrology in such areas as remote sensing, chemical analysis and quantification, generation of precision RF and microwave signals, medical diagnostics, length standards, atomic clocks, and references for exoplanet identification and characterization, with new applications appearing continuously. Frequency combs are also ubiquitous in the research laboratories of universities and in national laboratories.
The interplay with and impact on applied physics is also apparent. Improved optical frequency standards will find use in fields that traditionally rely on precision timing (navigation, electronics, communications, and spectroscopy), but in more extreme ways. Such possibilities might include deep space travel and optical-based circuitry and ultraprecision timing for science experiments (e.g., at accelerator centers). The TFD has sent a frequency-comb system to the McDonald Observatory in Texas to aid in the search for exoplanets.
Quantum degenerate gases include Bose-Einstein condensate, Fermi condensates, and molecular gases. In addition to providing a unique laboratory for fundamental physics, scientists across NIST use quantum degenerate gases for quantum information (QI) processing research, quantum simulation, and ultrahigh vacuum standards, with new applications continually evolving.
Division scientists demonstrated cooling to the quantum ground state of a macroscopic object. This system is a promising candidate for quantum information processing, and for ultrasensitive transducers.
Another area of research is observation of spin exchanges in ultracold potassium-rubidium (KRb) molecules inside an optical lattice (a crystal of light formed by overlapping laser beams). In solid materials, such spin exchanges are the building blocks of advanced materials and exotic behavior. Observation of spin swapping could have an impact on future research in such diverse areas as high-temperature superconductivity, energy transport through biomolecules and in chemical reactions,
spintronics (a new kind of microelectronics), and the physics of liquids and solids. The work on spin exchange of ultracold molecules is a new testing ground, enabled by tools that have been developed at the division. It will address fundamental questions of molecule–molecule interactions and can be used as a quantum simulator of many-body spin dynamics.
The group of Eric Cornell is using trapped molecular ions to search for a possible electric dipole moment of the electron. This experiment is one of several other ongoing efforts worldwide. The potential for non-point structure of the electron has deep implications for fundamental physics, cosmology, the apparent imbalance between matter and antimatter, and many other issues. The Cornell team has pushed in the 10−28 uncertainty range, where possible EDM (electric dipole moment of the electron) effects may be just detectable and is poised to push into the unexplored 10−30 range.
There is a strong theory effort in the division. One of the more exciting areas is understanding the realization of quantum Hall states via synthetic gauge fields generated by a spatially dependent optical coupling between internal states of the atoms. One current topic is how to suppress or control collisional relaxation decoherence as well as alternative ways of generating strong Abelian and non-Abelian gauge fields.
Stable laser systems have long been defined by John L. Hall and coworkers. The early days of this work used, for example, locking to the Lamb dip; the work has progressed far beyond the early stages. Work is being conducted on unique ultrastable laser technologies, including the development of an ultrastable reference cavity comprising a monolithic silicon crystal with unique end mirrors and on reducing sensitivity to cavity perturbations. This is used to lock the laser while the signal from an atomic clock is being acquired. Such a device is often called a flywheel because it provides excellent short-term stability to the laser. This work is important in a variety of fields, including experimental relativity and the laser gyro.
Cold atom and stable laser physics is an important area of research. While there are some early-known quantum many-body phenomena with clear impacts (for example, quantum magnetism and superconductivity), the biggest impacts are likely to come from phenomena not yet known or observed. The division strives to play a leadership role in this new frontier, in both experiment and theory, while still leveraging research and measurements using the many important single-body (individual) quantum phenomena.
A fascinating development is the creation of a unitary quantum converter that can interconvert microwave and visible radiation. This advance, while limited by the need for extreme temperatures (40 mK), could eventually have wide-ranging implications for the Internet and other applications. Scientific applications that can eventually benefit from it include clock-signal distribution and QI transfer. As noted in a 2014 commentary,1 “The potential to transfer QI between optical and microwave photons is especially exciting to the QI processing community. Superconducting microwave circuits have shown great promise for quantum computing, while quantum optics is better at transmission and quantum measurements—combining the two would vastly expand our ability to process and communicate information at the quantum level for computing and security purposes.” This effort is at the cutting edge, and it is not known where it will go, but the potential seems large. It is an example of the kind of work one hopes for from JILA.
Biological physics in the division has had a varied path, including the development of technologies to probe the real-time dynamics and kinetics of large, single biological molecules such as proteins, enzymes, and nucleic acids, to better understand normal physiology and disease processes. These are large areas of science being conducted worldwide. There are technical barriers that can arise and that need innovative measurement science, to which the division has been a contributor. Historically there are examples of the application of measurement science within the field of biological physics, one of which is described below, but there are new capabilities emerging that will broaden the scope if further encouraged.
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1 M. Tsang, 2014, Microwave photonics: Optomechanics sets the beat, Nature Physics 10:245-246.
As a historical example in biological physics, targeted chemotherapy often exploits a genetically engineered monoclonal antibody (mAb) that is chemically attached to an agent that can kill tumor cells. Monoclonal antibodies are designed to attach to specific antigens (e.g., proteins) that are predominantly found on the surfaces of malignant cells, and mAb’s can be engineered to bind to them. Once research determines that a certain cell-surface molecule indicates cancer, then mAb’s can be designed to target that molecule and hence the cell that it is on. One way to target therapy is to conjugate radioactive atoms to the mAb’s, using the radiation to treat the tumors. This radioimmunotherapy received FDA marketing approval in 2009. However, before FDA could approve the marketing of radioactive materials (e.g., yttrium-90) there needed to be a measurement system in place to ensure that the intended dose of radiation was delivered. The PML Radiation Physics Division was instrumental in getting this done, holding workshops so that the relevant stakeholders agreed on what procedures were needed, and providing an anchor in the quality system—a yttrium-90 radioactivity standard solution. This is an excellent example of how research crosscutting physics and biology is being carried out at NIST.
Another example in biological physics has been the development of the world’s most stable atomic force microscope (AFM) for biophysical applications, such as exploring the folding landscape of biological macromolecules in solution or in biological membranes. Because the measurements are in aqueous environments at physiologically relevant temperatures, the 100- to 1,000-fold gain is relevant for the biology. While the division’s AFM technology is currently aimed at following the complex behavior of proteins and nucleic acids in real-world biological systems, it is also available for a broad range of physical measurements. It is significant that one of the leading laboratories is seeking to duplicate the instrument, and the division is helping it to do so.
AFMs are also being developed for the study of structure–energy relationships in biological macromolecules and membranes. When biological macromolecules are synthesized, they are linear polymers that must fold to make specific compact structures before they can function in cells. There has been limited work to optimize AFM methods to follow the energetics and intermediate states of protein folding. This has presented an opportunity for a laboratory focused on metrology to pick apart the technique, identify the weaknesses, and fix them. The result is an orders-of-magnitude improvement in stability and sensitivity that opens up new capabilities and is likely to allow new explorations of protein folding, a missing conceptual link in the expression of genetic information. In the fields of biological membranes and macromolecular folding, energy landscapes can now be explored as a set of equilibrium measurements that were inconceivable before the JILA advances. The current results on the folding of a membrane protein are particularly interesting and are unmatched by those in any other laboratory in the world.
The world’s fastest system for measuring and separating individual living cells with unique properties revealed by ultrafast optical studies has been demonstrated for activities such as quickly identifying algal cells with the highest biofuel production and rapidly identifying optimal fluorescent proteins used to monitor real-time processes in living cells. Practical uses of biological systems are often assisted by finding the optimal organisms in a diverse population, so this technology will find important applications.
PORTFOLIO OF SCIENTIFIC EXPERTISE
In terms of its core strengths, the QPD includes an elite collection of scientists—so elite that it is a constant problem to protect the Fellows from recruitment by other organizations. Unfortunately, the salary of NIST employees is often not able to compete with salaries at academic institutions.
Along with recruitment by other organizations will be the problem of replacing the senior JILA Fellows as they retire. The division is moving strongly into research and measurements on quantum many-body phenomena as the key thrust of the second century of quantum mechanics. Single-body (individual) quantum phenomena have been enormously successful and powerful.
The division does not seem to have a consistent and clear approach to the use of intellectual property. In some fields, the use of a patent by a research organization can be to facilitate new companies that can be protected in their exploitation of the kinds of technology developed at the division. It appears that there has been no consistent view, and that the expertise to guide a technology transfer effort is not in place. Division investigators are, understandably, confused, asking, “Are we patenting this year?” An organized position needs to be thought through for the future—either intellectual property is useful and important or not, in the areas represented. A serious effort is a large expense, so the division will need to seek support from PML if the decision is to protect the intellectual property.
ADEQUACY OF FACILITIES, EQUIPMENT, AND HUMAN RESOURCES
JILA has a very slow turnover rate, perhaps because it recruits excellent faculty and make them happy. Faculty hired more than a decade ago are still referred to as new, and the slow turnover makes the initiation of new areas, such as biological physics, challenging. There will probably be, it seems, a tension between maintaining current directions and creating new ones. The following findings confirm those of the previous (2010) review of the division2:
- The new JILA X-Wing provided the space needed to expand present crowded laboratories and make vibration-free areas and, hopefully, clean rooms available for ultrafast and other experiments. The JILA shops provide service that is unmatched in pure university environments in the design and construction of various types of mechanical and electronic equipment, and it is critical that they be maintained at that high level.
- The current size of JILA is nearly optimal, given expectations for future financial resources and space and in recognition of the challenges of maintaining a coherent organization as the organization’s size increases. JILA does not expect to grow appreciably in the foreseeable future. Instead, it will focus on improving the balance of various research areas through replacements as fellows retire or otherwise leave JILA.
DISSEMINATION OF OUTPUTS
The following findings confirm those of the previous (2010) review of the division3:
- The impact of the QPD is outstanding as measured against its stated goal and mission of making important advances at the frontiers of science that enable future precision measurement technology and producing graduates who form a talented pool of scientists who are now dispersed throughout the NIST laboratories and elsewhere. These researchers are also having significant impact through applications of their technology outside NIST—for example, in sensitive, high-resolution frequency comb spectroscopy for trace detection and molecular fingerprinting and in the development of technology for multiplexed low-temperature detector arrays for astronomy.
- The division is a premier laboratory that favorably competes, in most of the fields of research that it pursues, with the best academic and federal research institutions in the world, and the graduate school of the University of Colorado was recently ranked in a national rating as number one in atomic physics. The laser frequency comb work and the cold atom and now the new cold molecule research are among the best in the world. The division has attracted
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2 National Research Council, Assessment of the National Institute of Standards and Technology Physics Laboratory: Fiscal Year 2010, The National Academies Press, Washington, D.C., p. 52.
3 Ibid., p. 50.
applicants with competing offers from top-five U.S. institutions in areas identified for expansion, such as biological physics and nanoscale physics.
JILA alumni have started about a dozen high-tech companies in such areas as optical components, medical diagnostics, and gravity meters. These companies provide innovative technologies and good jobs, commensurate with the NIST mission to facilitate economic growth and new technologies. JILA alumni are key scientific and innovation leaders in industry laboratories, in universities, and in national laboratories (beyond NIST). They contribute broadly to U.S. economic growth and technology development, and they expand the active network of collaborators for NIST.
CONCLUSION
The Quantum Physics Division has had a spectacular run of success over the past 20 years, and long-range planning will be needed to guide continued success. The move into quantum many-body phenomena with strong theoretical support is important so that the division will remain at the frontier of quantum physics. However, the role that quantum-nano biological physics plays in the division needs to be carefully considered. The biological physics effort presently has very little quantum physics. While the current faculty are outstanding, biological physics will need additional hires if it is to become on par with the level of effort of other areas in this division.
Given the promising developments such as those described above, it seems that some expansion is warranted, subject to the reality of budget constraints.
