6
Quantum Physics Division

MISSION

The goal of the Quantum Physics Division is to make transformational advances at the frontiers of science, in partnership with the University of Colorado at JILA. (JILA is a joint research institute of CU and NIST that is engaged in research in the areas of the physical sciences. It is supported by both CU and NIST, and its administration is overseen by a chair who is selected every 2 years, alternating between individuals from CU and NIST.) The Quantum Physics Division’s mission includes helping to produce the next generation of scientists and to investigate new ways of precisely directing and controlling light, atoms, and molecules; measuring electronic, chemical, and biological processes at the nanoscale; and manipulating ultrashort light pulses.

SCOPE

The Quantum Physics Division, located at JILA on the campus of the University of Colorado in Boulder, has 4 NIST fellows, 13 scientists/engineers, and 3 administrative support staff, as of January 2010. Its FY 2009 budget was about $10.0 million, 77 percent of which was STRS funding.

The strategic elements of the Quantum Physics Division are as follows:

  • To develop measurement science tools and their applications to technology;

  • To exploit Bose-Einstein condensation, quantum degenerate Fermi gases, and cold molecules for metrology and ultralow-temperature physics;

  • To advance ultrafast science and apply it to physics and biophysics;

  • To apply cutting-edge measurement science to biological systems;

  • To apply laser spectroscopy to important problems in chemical physics and biophysics; and

  • To educate a supply of top-quality scientists for NIST and elsewhere.

PROJECTS

Essentially all of the research projects pursued by the Quantum Physics Division are very well conceived and conducted, and proven to be relevant to and enhancing of the stated mission of the Physics Laboratory and NIST. The atomic and molecular physics at JILA has received top rating by U.S. News and World Report. Projects are described in detail in the section “Major Projects,” below.



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6 Quantum Physics Division MISSION The goal of the Quantum Physics Division is to make transformational advances at the frontiers of science, in partnership with the University of Colorado at JILA. (JILA is a joint research institute of CU and NIST that is engaged in research in the areas of the physical sciences. It is supported by both CU and NIST, and its administration is overseen by a chair who is selected every 2 years, alternating between individuals from CU and NIST.) The Quantum Physics Division’s mission includes helping to produce the next generation of scientists and to investigate new ways of precisely directing and controlling light, atoms, and molecules; measuring electronic, chemical, and biological processes at the nanoscale; and manipulating ultrashort light pulses. SCOPE The Quantum Physics Division, located at JILA on the campus of the University of Colorado in Boulder, has 4 NIST fellows, 13 scientists/engineers, and 3 administrative support staff, as of January 2010. Its FY 2009 budget was about $10.0 million, 77 percent of which was STRS funding. The strategic elements of the Quantum Physics Division are as follows:  To develop measurement science tools and their applications to technology;  To exploit Bose-Einstein condensation, quantum degenerate Fermi gases, and cold molecules for metrology and ultralow-temperature physics;  To advance ultrafast science and apply it to physics and biophysics;  To apply cutting-edge measurement science to biological systems;  To apply laser spectroscopy to important problems in chemical physics and biophysics; and  To educate a supply of top-quality scientists for NIST and elsewhere. PROJECTS Essentially all of the research projects pursued by the Quantum Physics Division are very well conceived and conducted, and proven to be relevant to and enhancing of the stated mission of the Physics Laboratory and NIST. The atomic and molecular physics at JILA has received top rating by U.S. News and World Report. Projects are described in detail in the section “Major Projects,” below. 43

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STAFFING The division and JILA expect that the current number of 29 JILA fellows will remain approximately constant. But many of the current fellows are in the early stages of their careers, and both their expressed plans and historical trends indicate that their group sizes are likely to grow significantly, as allowed by the new space added by the new building. JILA and the Quantum Physics Division have an excellent shop infrastructure, including the following:  An advanced instrument shop with seven highly experienced and capable instrument makers. The JILA instrument shop participates directly and substantially in designing complex instruments, based on general ideas and needs expressed by the researchers.  An advanced electronics shop, with five experienced and talented staff. As with the instrument shop, electronics shop staff design complex systems based on general descriptions of need from the researchers.  An experienced and capable information technology staff providing direct support to complex computing needs (clusters, etc.) and interfacing equipment with computers.  A highly qualified administrative staff helping to manage the complex activities of JILA, including crucial grant application processes. The success of division and JILA scientists is dramatically aided by this infrastructure, and the students and postdoctoral researchers training at JILA obtain a unique educational advantage through their close interactions with expert instrument makers, electronics designers, and IT staff. This substantial infrastructure is supported by all JILA researchers—in the division and at CU—and any loss of the infrastructure would be highly detrimental to the division. However, the state of Colorado is facing a severe budget shortfall, as is the case for most states, and state funding for the university is gravely threatened. The University of Colorado is facing a severe budget cut in FY 2011, after making significant cuts in FY 2009. If this results in a significant reduction in CU funding to JILA, the research infrastructure (instrument shop, electronics shop, IT shop, administrative support) should be protected as much as possible, as this infrastructure is a unique contributor to JILA’s excellence. MAJOR EQUIPMENT In addition to the shop infrastructure and staff component discussed in the section “Staffing,” above, new, significant equipment purchases are also important to the division’s ongoing and future work. American Recovery and Reinvestment Act funds are being used to purchase a new state-of-the-art femtosecond laser system; a new state-of- the-art atomic force microscope; and a new state-of-the-art scanning electron microscope (SEM) with a resolution of 1.0 nm, imaging voltages from 200 V to 30,000 V, a precision stage with five-axis motion control, and capability for electron beam lithography (EBL). 44

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The new SEM/EBL will not only substantially improve imaging capabilities for nanotechnology applications, but will also provide new precision fabrication capabilities to extend nanotechnology research and measurements further. FACILITIES It is clear that inadequate facilities have severely hampered the progress on and efficiency of research in the Quantum Physics Division in two major areas: (1) Poor control of air temperature, air cleanliness, vibration, and other environmental conditions in the outdated laboratories has seriously compromised precision measurements. (2) Insufficient laboratory and office space prevents the expansion of research activities. The staff provided suggestions of factors that hinder research:  “We’ve come to a point where we could progress faster if we had a laminar flow of dust-free air over our optical tables. We’re holding off on installing this technology pending resolution of uncertainties about the new building.”  “Temperature control has been an issue.”  “Space is limited.”  “Our state-of-the-art AFM is housed in an unrenovated basement dating back to 1962 with all the expected problems with temperature stability and noisy ventilation.” These are indeed serious issues. The planned JILA expansion should help solve the problem with lack of space overall, and should resolve the environmental problems for those fortunate enough to move into the new laboratories. However, the new building creates two pressing needs for funding, namely:  Costs of moving complex laboratories into the newly constructed space, and  Renovations of the existing laboratories to bring them up to current standards—especially urgent because it is easier to renovate the laboratories vacated by the move before staff moves back in. NIST and the University of Colorado should be working together to identify sufficient funding for both the relocation and the start of renovations of vacated laboratories in FY 2012. ANCILLARY SUPPORT AND RESOURCES There is always the problem in a very successful program such as the Quantum Physics Division and JILA that the fellows become ingrained. In the past, JILA had a vigorous Visiting Fellows Program funded by the division that brought top scientists from around the world to work at JILA for periods of a few months to a year. This program was highly effective in the past for both JILA and the visitors. An active JILA Visiting Fellows Program provides the opportunity to spread knowledge, insights, technology, and NIST culture more widely and to bring new knowledge, insights, and 45

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technology into NIST. Over the past decade or so, the number and quality of interested visitors have significantly declined, and the value of the Visiting Fellows Program has likewise declined. Staff offered the following comment regarding this decline in the fellows program:  “If I were to put in a personal word, I would say that the JILA Visiting Fellows Program has been substantially reduced over the past 10 years, due to understandable budgetary pressures. However, this is a program which has traditionally gotten absolutely top scientists (say, in chemical physics) to come on sabbatical and work with us in our labs—this has a superbly nonlinear impact on how quickly science proceeds and evolves into exciting new areas at JILA and should be supported as best as one can.” That comment suggests that this aspect of the success of the Quantum Physics Division is being neglected. MAJOR PROJECTS Ultracold Atoms and Molecules In the area of ultracold atoms and molecules, a dramatic experiment has converted highly interacting pair states of colliding cold atoms into polar molecules in their lowest bound state by removing the appropriate energy with an optical Raman process. This opened up the field of ultracold single state-to-state chemical reactions. Reaction rates have been dramatically changed by polarizing the molecules with electric fields, changing the internal hyperfine state, and raising the temperature. Work continues on a difficult, high-payoff experiment to measure the dipole moment of the electron in a trapped polar molecule. This experiment has the possibility of contributing to fundamental extensions of the Standard Model of high-energy physics. The work has also involved the study of fundamental elementary excitations of a Bose- Einstein condensate such as vortices. Another example is the confinement of a BEC in two dimensions to access the interesting (and somewhat controversial) physics that happens in restricted geometries. Ultracold clouds of Fermi atoms are also studied. In this system correlated pairs of atoms form, and the pairs can Bose condense, similar to the formation of Cooper pairs in a superconductor. The ability to tune the pair interaction has led to a wealth of phenomena. In one experiment, a sudden pulse of magnetic field puts pairs of atoms into a novel quantum superposition, which oscillates in time between bound and unbound states. Another study explores the variation from the BEC regime, where localized pairs could form a Bose condensate to the Bardeen-Cooper-Schrieffer (BCS) regime, where pair formation is mediated by the surrounding condensate atoms and the size of the pair could become very large. This BEC-BCS crossover is important theoretically, and its understanding could impact the theory of high-critical-temperature (Tc) superconductivity. This work has 46

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been enabled by novel techniques developed for extracting information on the pair correlations from noise in absorption images of the cold atomic cloud. Development of New Systems and Techniques in Frequency Measurement The laser frequency comb has produced a revolution in optical frequency measurement and is key to the development of ultra-stable optical atomic clocks. Current work in the Quantum Physics Division applies the frequency comb technique to a new atomic clock system composed of an optical lattice of laser-cooled strontium atoms. This novel optical clock features a large number of atoms responding identically, thus providing the precision of a single atom with enhanced signal-to-noise ratio. Fractional frequency instability of 1.5 × 10-17 has already been achieved. The frequency comb is also being extended to the VUV and is approaching 50 nm. Another experiment addresses a problem of fundamental interest and great applicability, that of measuring the center of a resonance line to better precision than is allowed by the shot noise due to having only N atoms. Modern techniques of quantum information have provided routes to this; a squeezing approach is being adopted and is close to demonstration. Approaching Quantum Limited Nanoscale Mechanical and Electronic Measurement In the effort of approaching quantum limited nanoscale mechanical and electronic measurement, the quantum limits to microwave measurement, amplification, and interferometry are tested in a series of elegant experiments that use novel microwave interferometers and nonlinear Josephson devices to explore the concept of microwave quantum optics. A microwave Fabry-Perot interferometer has been fabricated containing the microwave equivalent of a nonlinear Kerr medium composed of a metamaterial built from a series of 400 Josephson junctions. This device is a phase-sensitive parametric amplifier, capable of the near-noiseless amplification of one quadrature of a microwave signal. It can also be used to generate squeezed states of the microwave field, and as much as 85 percent phase-dependent noise suppression has been observed. Using related technology, a low-noise, superconducting quantum interference device (SQUID) multiplexer has been developed for the readout of arrays of low- temperature astronomical sensors. This multiplexer has the potential to read out an array of thousands of detectors in a single channel with gigahertz bandwidth, and could have application to novel detector arrays used in nuclear and particle physics, materials science, and astronomy. Ultrashort Femtosecond Laser Pulse Interactions with Matter The work on ultrashort femtosecond laser pulse interactions with matter is divided into three areas: interactions between alkali atoms in the gas phase, condensed-matter systems, and spintronics dynamics. In the gas dynamics work, the effort is primarily on the study of the collision dynamics of potassium atoms. Potassium atoms are illuminated with a sequence of two 47

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pulses. The first excites the atom to a specific state, and the second has a frequency that is absorbed only by the excited atoms and thus induces emission, as long as the excited atoms have not lost their energy by collision. The intensity variation as a function of delay provides a measure of collision dynamics. The condensed-phase work involves cross-correlation two-dimensional near-IR spectroscopy of excitons in semiconductors using three, femtosecond, near-IR pulses to generate excitons in semiconductors such as gallium arsenide (GaAs). The correlation between absorption and emission was determined in a plot of wave patterns and frequency. This two-dimensional spectroscopy method is capable of determining correlated oscillation of two groups in a molecule or lattice. Using this rather new two- dimensional spectroscopic method, the structure of groups of large biological molecules and also the electronic properties of semiconductors may be revealed, which would be impossible when only the normal one-dimensional spectroscopic methods are used. The knowledge obtained on GaAs and other semiconductors by this method may lead to better electronic devices. This work is at the leading edge of work in the broader community. The spintronics work involves developing the capability of maintaining electron spin direction for several nanoseconds while being transported micron distances, and is of paramount importance for high-capacity storage and other devices. A group at JILA has determined that the spin direction is more stable when confined in the defects of semiconductors and that it loses alignment fast when embedded in a perfect single-crystal environment. It was determined that the place of highest spin stability is located in a crossover “magic” point somewhere between perfect crystal and defect. This work is also leading edge. Laser Spectroscopy Kinetics and Dynamics of Organic Molecular and Nanoparticle Systems The area of laser spectroscopy kinetics and dynamics of organic molecular and nanoparticle systems involves ultrashort, femtosecond laser pulse interactions with matter and has a close connection with chemistry and biological physics that is described below. The techniques determine basic chemical-reaction dynamics by means of laser spectroscopy of jet-cooled molecular ions and radicals, intermolecular energy surfaces, and low-temperature radical and ion dynamics. In addition, a considerable effort is made in the study of single-molecule kinetics and microscopy. These techniques have been used to study single quantum dot emission kinetics of cadmium sulfide and silver involved in nanoparticle lithography. This group has been very active and is successful in the design of new equipment and devices and the improvement of standard equipment for use in specific experiments. For example, it developed, designed, and built a novel, near-field, apertureless scanning optical microscope capable of less than 10 nm resolution that finds use in many areas of physics, chemistry, and biology. Utilizing their slit jet discharge spectrometer, the researchers have studied high-resolution vibrational spectra of jet-cooled large organic radicals that were obtained for the first time. 48

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Biological Physics The two main biological physics groups have quite different areas of expertise and interact with different groups within JILA and at the University of Colorado. Both groups study single molecules, but the second group uses fluorescence energy transfer techniques whereas the leader of the first group is a world expert in the use of optical tweezers and lately of atomic force microscopes in the incredibly precise measurements of subnanometer motions of biological molecules. This researcher’s recent work on the molecular motor RecBCD (a protein consisting of three polypeptides RecB, RecC, and RecD) is an example of how much is yet to be learned about how nanomotors move along biological polymers. The questions of the step sizes of these motors, the role of thermal noise, and the basic physics of very small displacement measurements all come into play here. The first main group in biological physics is working to improve the resolution of optical tweezers by increasing sensitivity while reducing system noise, which is clearly connected to the JILA tradition of precision measurements. This group has explored the use of a more stable optical design (with improved laser-pointing stability and reduced microscope-stage drift), active sample stabilization, and the introduction of a grid of nanofabricated fiducial marks. One researcher with this first group has made significant progress in the past 2 years. His microfluidic work, aimed at increasing the ability to screen fluorescent proteins, is an important and needed means for the judicious selection of the appropriate fluorescing proteins from the rather vast collection available. The work on single- molecule spectroscopy, microscopy, and dynamics is very interesting research but not unique; nonetheless, it has the potential of yielding surprising, excellent data. This researcher’s ultrafast research would be enhanced by closer collaboration with one of the laser groups—but not enough to provide the system(s) and the in-depth expertise that he needs to perform the rather intricate structural and dynamics experiments on biological systems that he is pursuing. The second group described above has built on its expertise in single-molecule optical detection to elucidate the folding conformational thermodynamics of single ribonucleic acid (RNA) molecules and single DNA molecules in electrophoresis. The group has used fluorescence energy transfer techniques at the single-molecule level to measure distances of 2 to 8 nm between specifically labeled sites on the RNA. This information is crucial to understanding RNA-based enzymes, or ribozymes. In the future, the group’s techniques should make it possible to probe the folding and unfolding of biomolecules in chemically active states. Finally, an outstanding example of the cross-fertilization of technologies developed at JILA for the core mission of the development of measurement science tools is the extension of John Hall’s Nobel Prize-winning work on optical combs to another researcher’s application of this technology to biomolecule detection. This research group invented cavity-enhanced direct frequency comb spectroscopy, and it has shown that it can perform ultrasensitive detection of unknown chemicals. It has recently developed a more sensitive, smaller, and less costly fiber laser for this system, which can perform ultrasensitive and fast detection of organic molecules using a simple charge-coupled- 49

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device camera, opening the door for using this technique for medical and for homeland security applications. ASSESSMENT OF THE DIVISION Following is the summary of the panel’s assessment of the overall quality of the Quantum Physics Division (including opportunities for improvement) in terms of the three criteria as requested by the NIST Director (see Chapter 1). Assessment Relative to Technical Merit The Quantum Physics 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 definitely among the best in the world. The division has attracted applicants with competing offers from top-five U.S. institutions in areas identified for expansion, such as biological physics and nanoscale physics. Assessment Relative to Adequacy of Resources Facilities remain a problem for the continued excellence of the division. The new building should provide the needed space to expand present crowded laboratories and make vibration-free areas and, hopefully, clean rooms available for ultrafast and other experiments. The JILA shops, by general opinion, 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 absolutely critical that they be maintained at that high level. However, there are severe financial pressures being exerted on the division that must be addressed, as noted above. Assessment Relative to Achievement of Stated Objectives and Desired Impact The impact of the Quantum Physics Division 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 in producing graduates that 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. 50

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Additional Considerations The comments and recommendations resulting from the panel’s 2008 visit to the division were very seriously considered both by the Quantum Physics Division and by NIST. In the 2008 review, the panel expressed three key concerns, which are identified below, along with the Quantum Physics Division’s 2010 response. 1. The first concern expressed by the panel in the 2008 review: The increased emphasis on nanotechnology needs to be supported by upgrades to better instrumentation, especially an improved scanning electron microscope with a state-of-the-art field emission source. The existing SEM available to the Quantum Physics Division at JILA was evaluated not as state of the art, and it was proposed by the panel that JILA needed in-house a very high quality SEM for the imaging of the nanostructures and to do nanolithography. The response of the division: The American Recovery and Reinvestment Act funding for NIST equipment purchases includes funding for a new, state-of- the-art scanning electron microscope with resolution of 1.0 nm, imaging voltages from 200 V to 30,000 V, precision stage with five-axis motion control, and capability for electron beam lithography. The new SEM/EBL will not only substantially improve imaging capabilities for nanotechnology applications, but it will also provide new precision fabrication capabilities to further extend nanotechnology research and measurements. The procurement is underway at this time, and the group (Lehnert group) hopes to take delivery within several months. In addition to being used for the SEM/EBL, ARRA funds are also being used to purchase the following for the Quantum Physics Division:  A new, state-of-the-art femtosecond laser system to support research and measurements on the structure and dynamics of enzymes that could be used for the high-efficiency production of biofuels and to extract cleaner energy sources from petroleum and other fossil fuels;  A new, state-of-the-art femtosecond laser system to support research and measurements on the interaction of ultrafast laser pulses with solid-state systems and other matter; and  A new, state-of-the-art atomic force microscope for especially challenging measurements and research on biological samples in both air and fluid environments, with the best available control of positioning, temperature, and vibration isolation. In total, an estimated $1.7 million of new ARRA-funded research and measurement equipment is being procured to support Quantum Physics Division programs. 51

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2. The panel noted the following in its 2008 review: The interaction with the astrophysics group at the University of Colorado is of some concern; it should be enhanced and the number of researchers of this group should be increased. The response of the division: JILA fellows, representing both the University of Colorado and NIST researchers, have recently jointly agreed on a revised JILA strategic plan. One of the key issues identified in the plan is the need to improve integration of the collaborative astrophysics research into the other JILA activities. As one approach to this integration, the strategic plan identifies a preference for hiring an experimental astrophysicist who would focus on developing innovative imaging and measurement technologies. Such a new member of the division and JILA would be well positioned to help foster collaborations among the existing astrophysics research and other traditional strengths in JILA such as experimental atomic, molecular, and optical physics and experimental chemistry. There was also agreement among the group that 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. Thus 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. 3. The third issue raised by the panel in its 2008 review: Steps should be taken at JILA to ensure that space limitations do not create potentially unsafe working conditions detrimental to productivity. It was recommended that funding to build additional space be provided in a timely fashion. It was acknowledged that the Joint Quantum Institute had plans for a new building that would provide new laboratory space for the Laser Cooling and Trapping Group, and these plans should be brought to completion. The panel concluded that it was critical for the Quantum Physics Division that funding for the new JILA building be provided; the lack of space was detrimental to productivity, created potentially unsafe working conditions, and could affect the ability to attract and hire top-class scientists in the future. This was to be considered a top-priority item for this division. It was critical that funding for the new JILA building be put in place and that the plans for design and construction move forward. The response of the division: Construction of the JILA Expansion (also known as the JILA X-Wing) will begin in May 2010. The new building will add approximately 50,000 square feet of laboratory, office, and meeting space, expanding the total JILA space by about 50 percent. The new laboratory space will include high-performance labs with tight control of temperature, vibration, and air quality, to facilitate the most demanding research and measurements. 52

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The total cost of the new building is currently estimated at approximately $35 million, although the actual cost will not be known until final construction bids are received in late February 2010. NIST has already contributed $22.5 million to the construction, and the University of Colorado has committed to providing the balance of the required funds. Construction of the JILA Expansion is currently scheduled to begin May 2010, with building occupancy tentatively scheduled for January 2012. The additional space is planned to accommodate approximately 30 JILA fellows and their research groups, based both on polling of the current JILA fellows about their plans for group size and using historical trends. There are many early-career researchers among the current 29 JILA fellows, and their research groups are expected to grow significantly. Thus the JILA Expansion is intended to support the natural growth of research groups for the current fellows, but it is not intended to support a significant increase in the number of fellows. The growth in staff will be almost entirely among students, postdoctoral researchers, visitors, and other temporary staff. Meeting current standards of air cleanliness and temperature control and freedom from vibration in the new laboratories does nothing to improve the poor conditions in the old laboratory. Since the space vacated by groups moving to the new building is now empty, it is most economical to renovate its air system as soon as possible—certainly prior to moving new groups into that space. CONCLUSIONS AND RECOMMENDATIONS Conclusions The Quantum Physics Division remains one of the premier fundamental research physics laboratories in the world, a jewel in the crown for NIST and the Physics Laboratory. Although severe economic pressures are being brought to bear on NIST, the Quantum Physics Division, and JILA, at present there has been a strong response by NIST that will strengthen and maintain the level of excellence for the near future. The Quantum Physics Division has been growing in scope over the past few years, but this growth cannot continue forever, and there is concern that JILA cannot grow larger without sacrificing its strong sense of community. Atomic, molecular, and optical physics and biological physics should not continue to expand, but rather the Quantum Physics Division should maintain the present levels of excellence in its present fields of endeavor. Recommendations It is recommended that the Physics Laboratory should continue a high level of funding for the Quantum Physics Division, renovate the laboratories in the old building, increase the number of visiting fellows by shortening visits for one or two weeks, and seek both established experts and highly talented young researchers (e.g., postdoctoral researchers). 53