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Quantum Measurement Division

The Quantum Measurement Division (QMD) provides the physical foundation for the International System of Units (Système International d'Unités or SI), colloquially referred to as the metric system.

We achieve our goals through precision measurements of various fundamental constants — for example, realization of resistance and voltage through the quantum Hall effect and Josephson effect respectively, and through our determination of the best values of the fundamental constants done under the auspices of the Task Group on Fundamental Constants of the Committee on Data for Science and Technology (CODATA, an interdisciplinary unit of the Scientific Committee of the International Council for Science).

The division was heavily engaged in the redefinition of the SI that occurred in 2019. We supported that effort through R&D and through interactions with the International Bureau of Weights and Measures (BIPM) and its consultative committees including the Consultative Committee for Units (CCU), the Consultative Committee for Electricity and Magnetism (CCEM), and the Consultative Committee for Mass and Related Quantities (CCM).

As part of this effort, NIST constructed a new Watt Balance which — prior to the redefinition — was used to make one final precision measurement of the Planck constant. After the redefinition, it became the means for the realization of the kilogram in the United States.

The redefinition of the SI achieved the goal of turning it into a system based on fundamental constants and properties of nature. In fact, the redefined SI is largely based on quantum mechanics and its generalizations. including quantum electrodynamics.

As such, the strategy of the QMD is to:

  • investigate and exploit quantum behavior to create measurement tools and capabilities at and beyond the standard quantum limit
  • explore the basic capabilities of complex quantum systems to better understand what future quantum technologies will allow us to measure, compute, and simulate
  • exploit this knowledge to create the foundation to realize and disseminate mass, force, and electrical quantities and improve our ability to realize these quantities
  • disseminate these quantities from first principles, through specially developed instruments and methodologies, or through scaling that minimizes the loss of accuracy of the various technologies involved relative to the best available quantum or classical technology
  • to create critically evaluated data relevant to both fundamental constants and atomic properties

Redefining the Kilogram

K20 prototype mass

For more than a century, the kilogram (kg) — the fundamental unit of mass in the International System of Units (SI) — was defined as exactly equal to the mass of a small polished cylinder, cast in 1879 of platinum and iridium.

Kept in a triple-locked vault on the outskirts of Paris, the platinum-iridium cylinder was officially called the International Prototype of the Kilogram (IPK). It even had a nickname: Le Grand K (The Big K). The accuracy of every measurement of mass or weight worldwide, whether in pounds and ounces or milligrams and metric tons, depended on how closely the reference masses used in those measurements could be linked to the mass of the IPK.

That situation has changed radically. In November 2018, the international scientific community voted to redefine the kilogram, freeing it from its embodiment in one golf-ball-sized artifact, and basing it instead on a constant of nature. That transformation was as profound as any in the history of measurement. MORE

News and Updates

Partially Unraveling an Entangled Mystery

Entanglement—a uniquely quantum phenomenon that intimately links the fate of subatomic particles even if they reside on opposite sides of the galaxy—is a key

Unity in the Photon Community

The creation and detection of single photons (the smallest units of light) has grown in a few decades from an experimental laboratory pursuit to an important

Projects and Programs

AC-DC Difference

The NIST Ac-dc 2 Difference Project performs leading edge measurement services and research for ac-dc difference measurements and dc voltage metrology. We

Applications of Quantum Information

Theory is being developed and used to devise methods for preserving and exploiting the quantum behavior of ever-larger systems for metrology, communication, and

Atomic Spectroscopy Data Center

Critical compilations of atomic energy levels, transition wavelengths, and transition probabilities. Online databases.

Calibration of Force Transducers

NIST provides calibration services for force-measuring instruments by applying known forces, compression, tension or both, to the elastic transducer and


Tools and Instruments


Press Coverage

A more perfect unit: the new mole

Popular Science
A video about the redefinition of the mole, featuring NIST's Savelas Rabb, Robert Vocke, and Stephan Schlamminger.


Sound Pressure Metrology Instrument And Determining Sound Pressure From Index Of Refraction

NIST Inventors
Richard A. Allen , Randall P Wagner , Benjamin Reschovsky and Akobuije Chijioke
A sound pressure metrology instrument determines sound pressure from index of refraction and includes: a light source that produces source light; the optical cavity that: receives an acoustic field from the sound source; receives the source light from the light source; produces acoustic-modified

Quantum-Enabled Flow Cytometer

NIST Inventors
Sergey Polyakov and Ivan Burenkov
Flow cytometry is arguably the most powerful optical method routinely used in the diagnosis of health disorders and disease monitoring. We enhance an optical flow cytometer with a photon­ number statistics measurement. Our technique allows for an absolute measurement of biomarker concentration and


Deputy Division Chief