Edit Proposal: Milestone-Proposal:First Atomic Clock You do not have permission to edit this page, for the following reason: You are not currently logged in. The action you have requested is limited to users in the group: Users. Please log in or create an account. Docket ID: (admins only) Thank you for proposing a technical achievement for possible recognition as an IEEE Milestone in Electrical Engineering and Computing. Your efforts help preserve the heritage of technology. Detailed information on the Milestone application process may be found at: Milestone Guidelines and How to Propose a Milestone. At least one of the proposer(s) must be an IEEE Member (including Student Member) in good standing. To the proposer’s knowledge, is this achievement subject to litigation? If the answer is "yes", the proposal cannot proceed further. Yes No You must be able to answer "yes" to all of the following questions. If the answer to any of the following questions is "no", the proposal cannot proceed further. Contact us at firstname.lastname@example.org if you are unable to answer "yes" to all of the following and would still like to proceed. Is the achievement you are proposing more than 25 years old? Yes No Is the achievement you are proposing within IEEE’s designated fields as defined by IEEE Bylaw I-104.11, namely: Engineering, Computer Sciences and Information Technology, Physical Sciences, Biological and Medical Sciences, Mathematics, Technical Communications, Education, Management, and Law and Policy. Yes No Did the achievement provide a meaningful benefit for humanity? Yes No Was it of at least regional importance? Yes No Has an IEEE Organizational Unit agreed to pay for the milestone plaque(s)? Yes No Has an IEEE Organizational Unit agreed to arrange the dedication ceremony? Yes No Has the IEEE Section in which the milestone is located agreed to take responsibility for the plaque after it is dedicated? Yes No Has the owner of the site given permission to place an IEEE plaque? Yes No Year or range of years in which the achievement occurred: Title of the proposed milestone. (Include date or date range in title. Example: “Alternating Current Electrification, 1886”) Please provide a plaque citation in English summarizing the achievement and its significance. Text absolutely limited by plaque dimensions to 70 words; 60 is preferable for aesthetic reasons. NOTE: The IEEE History Committee shall have final determination on the wording of the citation. Names of living persons are not normally used in citations. Exceptions to this are cases where the person's name is linked to the achievement itself (e.g. the Lempel-Ziv algorithm, Maxwell's Equations, etc.) or where the person's name is so widely recognizeable to the general public that it makes sense to use it. When used, the names should be the names of the engineers, scientists, or technologists who actually made the achievement, rather than managers or executives. For more information and suggestions about writing milestone citations, please visit Helpful Hints on Citations, Plaque Locations. The first atomic clock, developed near this site by Harold Lyons at the National Bureau of Standards, revolutionized timekeeping by using transitions of the ammonia molecule as its source of frequency. Far more accurate than previous clocks, atomic clocks quickly replaced the Earth’s rotational rate as the reference for world time. Atomic clock accuracy made possible many new technologies, including the Global Positioning System (GPS). In what IEEE section(s) will the milestone plaque(s) reside? Please specify the IEEE Organizational Unit(s) which have agreed to sponsor the Milestone, and supply name and contact information for the senior officer from those OU(s). Sponsorship has three aspects: 1) Payment for the cost of the plaque(s), 2) Arranging the dedication ceremony, and 3) agreeing to monitor the plaque and to let IEEE History Center staff know in case the plaque needs to be moved, is no longer secure, etc. Number 3 must be done by the IEEE Section(s) in which the plaque(s) is located, but aspects 1 and 2 can be done by any IEEE Organizational Unit, and they need not be the same one. Please note: your email address and contact information will be masked on the website for privacy reasons. Only IEEE History Center Staff will be able to view the email address. IEEE Organizational Unit(s) paying for milestone plaque(s) Unit: Senior Officer Name: E-mail: Unit: Senior Officer Name: E-mail: Unit: Senior Officer Name: E-mail: Unit: Senior Officer Name: E-mail: IEEE Organizational Unit(s) arranging the dedication ceremony Unit: Senior Officer Name: E-mail: Unit: Senior Officer Name: E-mail: Unit: Senior Officer Name: E-mail: IEEE section(s) monitoring the plaque IEEE Section: IEEE Section Chair name: IEEE Section Chair e-mail: IEEE Section: IEEE Section Chair name: IEEE Section Chair e-mail: Milestone proposer(s) Proposer name: Proposer email: Proposer name: Proposer email: Proposer name: Proposer email: Street address(es) and GPS coordinates of the intended milestone plaque site(s). Please include coordinates in decimal format rather than degrees. What is the intended site(s) of the milestone plaque(s) relation to the achievement? The intended site(s) must have a direct connection with the achievement (e.g. where developed, invented, tested, demonstrated, installed, or operated, etc.). A museum where a device or example of the technology is displayed, or the university where the inventor studied, are not, in themselves, sufficient connection for a milestone plaque. Also, please Describe briefly the intended site(s) of the milestone plaque(s). (e.g. Is it corporate buildings? Historic Site? Residential? Are there other historical markers already at the site?) Are the original buildings extant? Please provide the details of the mounting, i.e. on the outside of the building, in the ground floor entrance hall, on a plinth on the grounds, etc. How is the intended plaque site protected/secured, and in what ways is it accessible to the public? If visitors to the plaque site will need to go through security, or make an appointment, please give details as well as the contact information visitors will need in order to arrange to visit the plaque. Who is the present owner of the site(s)? In the space below, please describe in detail: the historic significance of the achievement, its importance to the evolution of electrical and computer engineering and science, its importance to regional/national/international development, its benefits to humanity, the ways the achievement was a significant advance rather than an incremental improvement of existing technology. The material submitted here will constitute the main descriptive article on the ETHW website for readers to learn about the milestone. Space is unlimited, and detail is encouraged. Most milestones require 1000 to 1500 words of support, however there is no word limit. The article should be readable by a wide audience that includes practicing engineers, scholars of history, and the general public. Some examples of the text of good milestone articles are First Radio Astronomical Observations Using Very Long Baseline Interferometry] and G3_Facsimile International Standardization of G3 Facsimile (Do not worry about the formatting of the page, IEEE History Center Staff will do that afterwards.) What is the historical significance of the work (its technological, scientific, or social importance)? The societal impact of atomic clocks has been immense. Many technologies that we take for granted rely on atomic clock accuracy, including mobile phones, Global Positioning System (GPS) satellite receivers, and the electric power grid. Atomic clocks fundamentally altered the way that time is measured and kept. Before atomic clocks, the second was defined by dividing astronomical events, such as the solar day or the tropical year, into smaller parts. This changed in 1967, when the second was redefined as the duration of 9 192 631 770 energy transitions of the cesium atom. The new definition meant that seconds were now measured by counting oscillations of atoms, and minutes and hours were now multiples of the second rather than divisions of the day. Atomic clocks also enabled astounding gains in timekeeping accuracy. For thousands of years prior to the invention of atomic clocks, the reference for world timekeeping was the Earth’s rotation rate, which was limited in accuracy to about one millisecond (one part in 10^8) per day. Quartz oscillators first appeared in the 1920s. The best quartz devices were eventually accurate enough to measure and record variations in the Earth’s rotation, but they were still limited in performance and sensitive to environmental changes. Atomic clocks provided a “quantum leap” in accuracy. Shortly after their invention, accuracies of parts in 10^10 became routine, and the accuracy of atomic clocks constructed at NBS and its successor, the National Institute of Standards and Technology (NIST), has increased by roughly one order of magnitude per decade as shown in the illustration below. [[File:Improvements in Atomic Clock Accuracy.jpg|700 px|]] The Scottish physicist James Clerk Maxwell was perhaps the first to recognize that atoms could be used to keep time. In an era where the Earth’s rotation was the timekeeping standard, Maxwell remarkably suggested to William Thomson (Lord Kelvin) that the “period of vibration of a piece of quartz crystal” would be a better absolute standard of time than the mean solar second, but would still depend “essentially on one particular piece of matter, and is therefore liable to accidents.” Atoms would work even better as a natural standard of time. Thomson wrote in the second edition of the Elements of Natural Philosophy, published in 1879, that atoms such as hydrogen or sodium are “absolutely alike in every physical property” and “probably remain the same so long as the particle itself exists.” Even so, atomic clock experiments didn’t begin until about sixty years after the suggestions of Maxwell and Thomson. The early experiments were finally made possible by the rapid advances in quantum mechanics and microwave electronics that took place before, during, and after World War II. Most of the concepts that led to atomic clocks were developed by Isidor Isaac Rabi and his colleagues at Columbia University in the 1930’s and 40’s. As early as 1939, Rabi had informally discussed applying his molecular beam magnetic resonance technique as a time standard with scientists at NBS. Rabi and his colleagues at Columbia first measured the cesium resonance frequency in 1940, estimating the frequency of the hyperfine transition as 9191.4 megacycles. This was relatively close to the number that would later define the second. Rabi’s work led to a Nobel prize in 1944, but atomic clock research at Columbia was mostly halted during World War II as scientists turned their attention to other areas and a demonstrable device was not built. Building on the accomplishments of previous researchers, Harold Lyons and his colleagues at NBS in Washington, DC began working towards the development of the first atomic clock in 1947. The NBS clock was based not on cesium atoms, but instead used the 23.8 GHz inversion transition of the ammonia molecule as its source of frequency. After a period of intense and rapid research and development beginning in the spring of 1948, the new clock was first operated on August 12, 1948 and was publicly demonstrated in January 1949. Although its accuracy was quickly surpassed by other atomic clocks, it marked the beginning of the era of atomic timekeeping. Photographs of first atomic clock: [[File:Ammonia_Clock_01061949.jpg|700 px|]] The world's first atomic clock as it appeared on January 6, 1949, the day of the first public announcement. An ammonia absorption cell consisting of about 8 meters of K-band waveguide is coiled around the round electric clock dial. The clock atop the equipment racks was driven by a 50 Hz signal obtained by dividing the signal from a quartz oscillator that was locked to the ammonia absorption frequency. However, its primary function was to let the world know that the new invention was indeed a clock. [[File:1949_Ammonia_Clock_Condon_Lyons.jpg|700 px|Condon (left) and Lyons (right) with Atomic Clock]] Dr. Harold Lyons (right), inventor of the ammonia absorption cell atomic clock, observes, while Dr. Edward U. Condon, the director of the National Bureau of Standards, examines a model of the ammonia molecule (1949). [[File:Condon_Lyons_Photo_25th_Anniversary_1974.jpg|700 px|Condon (left) and Lyons (right) with Atomic Clock on 25th anniversary]] A recreation of the original photo taken on the 25th anniversary of the atomic clock's invention. Dr. Harold Lyons (right), inventor of the ammonia absorption cell atomic clock, observes, while Dr. Edward U. Condon, the former director of the National Bureau of Standards, examines a model of the ammonia molecule (1974). [[File:1948 Ammonia Molecule Clock Backside.jpg|700 px|]] A 1948 photograph showing the backside of the first atomic clock and the electronic components contained inside the two equipment racks. Lyons is kneeling on the right. [[File:Ammonia_Clock_Smithsonian.jpg|700 px|First Atomic Clock on Display at Smithsonian]] The Division of Work and Industry of the Smithsonian Institute's National Museum of American History, holds the first atomic clock, constructed under Lyons’s direction at the National Bureau of Standards in 1948. The photograph shows the clock while on display at the museum. What obstacles (technical, political, geographic) needed to be overcome? The basic principles of atomic clocks were already well understood by researchers at the time of Lyon’s invention. In short, because all atoms or molecules (groups of atoms held together by a chemical bond) of a specific element are identical, they should produce the exact same frequency when they absorb energy or release energy. Thus, an atom or molecule could potentially serve as a “perfect” oscillator, and a clock referenced to an atomic oscillator would be far more accurate than previous clocks based on mechanical oscillations of a pendulum or a quartz crystal. Even though the potential advantages of atomic timekeeping were well known, many obstacles existed before an atomic clock could be built. Atomic transitions occurred in the microwave region, at much higher frequencies than had previously been measured, and systems and electronics were needed that could measure these frequencies by counting the atomic transitions. Determining the resonance frequency of a specific element was necessary so that it could be related to the second, the base unit of time interval. The next step would be to use the atomic resonance frequency to control the frequency of a physical oscillator, such as quartz crystal oscillator, by locking it to atomic resonance. Finally, to make the output of an atomic clock usable, the frequency of the locked quartz oscillator would need to be divided to frequencies low enough to utilize for keeping time. Lyons had chosen the absorption line of ammonia gas as the source of frequency for the first atomic clock, and his first obstacle to overcome was measuring the inversion transition frequency of the ammonia molecules. The ammonia gas was stored in an absorption cell, which was designed as a 30 foot long copper tube that was wrapped into a spiral. The measurement involved multiplying a signal from a 100 kHz quartz oscillator several times. The first stage consisted of a frequency multiplication chain built from low frequency tubes that resulted in a frequency of about 270 MHz. The second stage consisted of a frequency multiplying klystron (a linear beam vacuum tube), frequency modulated by a 13.8 MHz oscillator that multiplied the signal to about 2.983 GHz. Finally, the signal was multiplied to approximately 23.87 GHz by use of a silicon crystal rectifier. This frequency was fed to the ammonia absorption cell and tuned until the signal reaching a silicon crystal detector at the end of the cell dipped because of the absorption, as shown in the illustration. This dip indicated that the incoming frequency from the multiplication chain now matched the ammonia absorption frequency. When the “dip” occurred, an electrical pulse was generated. [[File:Ammonia_Absorption_Curve.jpg|700 px|]] The "dip" (shown on an oscilloscope) that occurred when the incoming microwave signal from the frequency multiplication chain matched the absorption frequency of the ammonia molecule. The next obstacle faced by Lyons and his group was developing a method to automatically adjust the quartz oscillator frequency until it matched the frequency of ammonia absorption line. This was done by taking a 12.5 MHz frequency from the quartz oscillator frequency multiplication chain and mixing it with the signal from the 13.8 MHz frequency-modulated oscillator. When the frequency from the mixer matched its expected value, another electrical pulse was generated. The time interval between the two generated pulses (the pulse from the absorption cell and the pulse from the mixer) was continuously measured. If the time interval was increasing it indicated that quartz oscillator frequency was increasing, and vice versa. The time interval measurements were used to generate a control signal that adjusted the quartz oscillator whenever necessary to keep it locked to the ammonia absorption frequency. The illustration shows a strip chart where the quartz oscillator was locked to the ammonia absorption frequency from 5 p.m. to 8 a.m. Before and after this period, the quartz oscillator was “unlocked” (free running). Each small division on the strip chart represents a frequency variation of less than 1 part per 10 million. [[File:Ammonia_Clock_Locked_Strip_Chart.jpg|700 px|]] A strip chart showing a period (from 5 p.m. to 8 a.m.) where the quartz oscillator was locked to the absorption frequency of ammonia. Another obstacle in building the atomic clock consisted of dividing the locked quartz oscillator frequency to low frequencies that could be used for timekeeping. The first atomic clock included dividers that produced two output signals, a 50 Hz signal that drove an ordinary synchronous motor clock, and also a 1000 Hz signal that was used to drive a special synchronous motor clock that was designed for comparisons with astronomical time (then the world standard for timekeeping) to within 5 milliseconds. The two block diagrams show the various components and functions of the first atomic clock, first in simplified form, and then in more detail. [[File:Simplified_Block_Diagram.jpg|700 px|]] A simplified block diagram of the first atomic clock. [[File:Complete_Block_Diagram.jpg|700 px|]] A complete block diagram of the first atomic clock. A final technical obstacle faced by Lyons was his quest to make his ammonia clock more accurate by increasing the quality factor, Q, which is the resonance frequency of an oscillator divided by the resonance width (or linewidth). Oscillators with higher Qs are potentially more stable and accurate, so it is desirable to increase Q as much as possible, either by using an atomic transition where the frequency is as high as possible, or by making the line width as narrow as possible. In the case of the ammonia clock, the resonance frequency was high (23.8 GHz), but the resonance width, or the range of frequencies over which the oscillator could resonate (represented by the dip in the absorption frequency shown above) was not particularly narrow. Thus, the potential accuracy of the ammonia clock was limited. Two versions of the ammonia clock were built, with the best reported accuracy about 2 ms per day (2 × 10-^8). Work on a third version was halted when it became apparent that cesium beam techniques were likely to provide a significant increase in accuracy. Even though the cesium resonance was not as high (9.192 GHz) there were numerous options available for decreasing the resonance width, leading to Q factors that were potentially much higher than those obtained with molecular absorption methods. As a result Lyons and his NBS colleagues turned their attention from ammonia to cesium clocks in 1950. What features set this work apart from similar achievements? Lyons was certainly not the first to perform spectroscopic frequency stabilization experiments or to engage in atomic clock research. He was just 35 years old at the time he first demonstrated the ammonia clock to the public in early 1949, and was a 25-year old graduate student when Rabi and his colleagues at Colombia first discussed employing their molecular beam resonance technique as a time standard. However, Lyons and his colleagues were able to rapidly move past the pure experimental stage and become the first to build a working atomic clock. The construction of an atomic clock in 1948 was a monumental engineering feat. In addition to the ammonia absorption cell, the new invention consisted of a number of electronic instruments including a quartz crystal oscillator, several stages of frequency multipliers, a frequency discriminator, and frequency dividers, integrated into a single system and housed in two large equipment racks. These instruments, along with the expertise obtained by NBS in several decades of maintaining and dissemination standard frequency signals, allowed Lyons to advance beyond what had previously achieved elsewhere. He was able to excite an ammonia absorption cell with the output of a frequency multiplier chain that could be measured against the national standard of frequency, quartz oscillators operated by NBS that were periodically calibrated against the astronomical time standards maintained by the U. S. Naval Observatory. This direct access to the best available time standards allowed Lyons to have confidence in his results and to verify that his new invention was working properly. Supporting texts and citations to establish the dates, location, and importance of the achievement. You must supply the texts or excerpts themselves, not just the references. Minimum of five (5), but as many as needed to support the milestone, such as patents, contemporary newspaper articles, journal articles, or chapters in scholarly books. At least one of the references must be from a scholarly book or journal article. 'Scholarly' is defined as peer-reviewed, with references, and published. The full reference, in English, must be uploaded, not just the citation. See below section for details on uploading material to the website. All supporting materials must be in English, or accompanied by an English translation. Patents: [P1] H. Lyons and B. F. Huston, "Atomic Clock," United States Patent 2,699,503 (Applied for April 30, 1949, granted January 11, 1955). [[Media:US_Patent_2699503.pdf]] Journal Articles: [J1] H. Lyons, "The Atomic Clock," Instruments, vol. 22, pp. 133-135, 174, December 1949. [[Media:Lyons_Instruments_Dec_1949.pdf]] [J2] "The Atomic Clock: An Atomic Standard of Frequency and Time," Journal of the Horological Institute of America, published in two parts in 1949 (issue 2, pp. 11-20 and issue 3, pp. 7-14). A copy of the original journal paper is not available but the text is identical to the following document, which is provided here: National Bureau of Standards, "The Atomic Clock: An Atomic Standard of Frequency and Time," NBS Technical Report 1320, 27 pages, January 1949. [[Media:NBS_Report_1320_1949.pdf]] [J3] H. Lyons, “The Atomic Clock: A Universal Standard of Frequency and Time,” American Scholar, vol. 19, pp. 159-168, April 1950. [[Media:Lyons_American_Scholar_1950.pdf]] [J4] H. Lyons, "Microwave Frequency Dividers," Journal of Applied Physics, vol. 21, pp. 59-60, January 1950. [[Media:Lyons_J_Applied_Physics_1950.pdf]] [J5] H. Lyons, “Spectral lines as frequency standards,” Annals of the New York Academy of Sciences, vol. 55, pp. 831-871, November 1952. [[Media:Lyons_New_York_Academy_1952.pdf]] [J6] H. Lyons, "Atomic Clocks," Scientific American, vol. 197, pp. 71-82, February 1957. [[Media:Lyons_Scientific_American_1957.pdf]] [J7] R. Beehler, “A Historical Review of Atomic Frequency Standards,” Proceedings of the IEEE, vol. 55, pp. 792-805, June 1967. [[Media:Beehler_Proc_IEEE_1967.pdf]] [J8] P. Forman, “Atomichron: The Atomic Clock from Concept to Commercial Product,” Proceedings of the IEEE, vol. 73, pp. 1181-1204, July 1985. [[Media:Forman_Proc_IEEE_1985.pdf]] [J9] M. A. Lombardi, T. P. Heavner, and S. R. Jefferts, "NIST Primary Frequency Standards and the Realization of the SI Second," NCSLI Measure: The Journal of Measurement Science, vol. 2, no. 4, pp. 74-89, December 2007. [[Media:Lombardi_Measure_2007.pdf]] [J10] M. A. Lombardi, "The Evolution of Time Measurement, Part 3: Atomic Clocks," IEEE Instrumentation and Measurement Magazine, vol. 14, pp. 46-49, December 2011. [[Media:Lombardi_IEEE_IM_Magazine_2011.pdf]] Conference Papers: [C1] H. Lyons, "Microwave spectroscopic frequency and time standards," Proceedings of the IXth General Assembly of URSI, paper no. 91, pp. 47-57, 1950. [[Media:Lyons_URSI_1950.pdf]] [C2] P. Forman, “The first atomic clock program: NBS, 1947-1954,” Proceedings of the 1985 Precise Time and Time Interval Meeting (PTTI), pp. 1-17, 1985. [[Media:Forman_PTTI_1985.pdf]] [C3] D. B. Sullivan, "Time and Frequency Measurement at NIST: The First 100 Years," Proceedings of the 2001 IEEE Frequency Control Symposium, pp. 4-17, 2001. [[Media:Sullivan_IEEE_FCS_2001.pdf]] Books: [B1] W. Snyder and C. Bragaw, “Achievement in Radio: Seventy Years of Radio Science, Technology, Standards, and Measurement at the National Bureau of Standards,” National Bureau of Standards Special Publication 555, October 1986. [[Media:Snyder_NBS_SP_555_1986.pdf]] [B2] C. H. Townes, "How the Laser Happened: Adventures of a Scientist," Oxford University Press: New York, 1999. [B3] T. Jones, "Splitting the Second: The Story of Atomic Time," Institute of Physics Publishing, Bristol and Philadelphia, 2000. News Articles: [N1] “The Atomic Clock: An Atomic Standard of Frequency and Time,” National Bureau of Standards Technical News Bulletin, vol. 33, no. 2, pp. 17-24, February 1949. [[Media:NBS_Bulletin_February_1949.pdf]] [N2] "Atomic Clock," Review of Scientific Instruments, vol. 20, no. 2, pp. 141-142, February 1949. [[Media:RSI_News_Release_Feb_49.pdf]] Miscellaneous: Cartoon, "Ripley's Believe it or Not!," King Features Syndicate, 1953. [[File:Figure_06_Ripleys_1953.jpg]] Supporting materials (supported formats: GIF, JPEG, PNG, PDF, DOC) which can be made publicly available on the IEEE History Center’s website (i.e. unencumbered by copyright, or with the copyright holder’s permission). All supporting materials must be in English, or if not in English, accompanied by an English translation. You must supply the texts or excerpts themselves, not just the references. Images and photographs are especially appreciated, however, it is necessary that you list the copyright owner for these and obtain the copyright owner’s permission to reuse. For documents that are copyright-encumbered, or which you do not have rights to post, email the documents themselves to email@example.com. Please see the Milestone Program Guidelines for more information. To add attachments, first upload the file and add by adding the text: [[Media:(filename)]] For example, if the file you uploaded was named "Milestone Reference.pdf", include the text: [[Media:Milestone Reference.pdf]] in the appropriate field. [[Media:2016-05-03 NIST Letter Support for Historic Plaque.pdf]] [[Media:Ivanov_Letter_from_Washington_IEEE_Section.pdf]] Please email a jpeg or PDF a letter in English, or with English translation, from the site owner(s) giving permission to place IEEE milestone plaque on the property, and a letter (or forwarded email) from the appropriate Section Chair supporting the Milestone application to firstname.lastname@example.org with the subject line "Attention: Milestone Administrator." Note that there are multiple texts of the letter depending on whether an IEEE organizational unit other than the section will be paying for the plaque(s). Submit this proposal to the IEEE History Committee for review. 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