Precision Electro-Mechanical Experiments (PREME)

Summary

The Precision Electro-Mechanical Experiments (PREME) program develops precision electro-mechanical measurements for fundamental traceability of the SI units and the determination of fundamental constants. By taking full advantage of the intrinsic scaling and multiple realization paths now offered by the new SI, PREME is developing projects for in-situ, fit for purpose direct realization of the SI units based on the defined values of the Planck constant, elementary charge, and the Josephson and von Klitzing constants. PREME has several projects, as discussed below.

Description

NIST-4 Kibble balance for the realization of mass in the range from 50 g to 2 kg.

NIST-4 Kibble Balance

Previously called ‘the Electronic Kilogram’ Project, a major component of PREME is the realization of SI unit of mass, the kilogram, using the NIST-4 Kibble balance, the fourth generation of Kibble balances at NIST. This is accomplished through a high-accuracy comparison of power as measured in mechanical (force and velocity) and electrical (voltage and resistance) units. Because of the quantum nature of all but the kilogram mass unit (laser length, atomic time, Josephson effect voltage, and Quantum Hall effect resistance), the two measurements provide a high-accuracy determination of a kilogram artifact based on the defined value of the Planck Constant.

In operation since 2015 NIST-4 has provided valuable data for the 2016 pilot study for the future realization of mass in the new SI, a final NIST value of the Planck constant for the CODATA Special adjustment of the fundamental constants for the assignment of the exact values of the defining constants that now form the foundational basis of the new SI, and the Key Comparisons of mass within the new SI.

Contact:
Darine Haddad
darine.haddad [at] nist.gov (darine[dot]haddad[at]nist[dot]gov)
301-975-6552

REFERENCES of Major Accomplishments:

“A macroscopic mass from quantum mechanics in an integrated approach”, F. Seifert et al, Nature Communications Physics, 5, Article number: 321, Dec 2022
https://doi.org/10.1038/s42005-022-01088-7

“Final report on the CCM key comparison of kilogram realizations CCM.M-K8.2021”, M Stock et al, Metrologia, 60(1A), Jan 2023
https://doi.org/10.1088/0026-1394/60/1A/07003

“Report on the CCM key comparison of kilogram realizations CCM.m-k8.2019,” M Stock et al, Metrologia, 57(1A):07030-07030, jan 2020
https://doi.org/10.1088/0026-1394/57/1a/07030.

“Measurement of the Planck constant at the National Institute of Standards and Technology from 2015 to 2017” D. Haddad et al, Metrologia, 54(5):633, 2017
https://doi.org/10.1088/1681-7575/aa7bf2

“A precise instrument to determine the Planck constant, and the future kilogram” D. Haddad et al., Invited article, Review of Scientific Instruments, 87(6), 2016.
https://doi.org/10.1063/1.4953825

“A LEGO Watt balance: An apparatus to determine a mass based on the new SI,” L S Chao et al., American Journal of Physics 83(913) 2015
https://doi.org/10.1119/1.4929898

QEMMS

The QEMMS Kibble Balance under construction.

Credit: NIST

The Quantum Electro-Mechanical Metrology suite (QEMMs) under development will provide Primary Standard Laboratories for quantum voltage, resistance, current, and mass traceable to the SI. The QEMMS Kibble balance has been designed as a single degree of freedom flexure-constrained motion. Using graphene quantum Hall resistance array standards (QHARS) developed by NIST that are capable of transport currents of 1 mA, it is now possible to combine Programmable Josephson Voltage Standards (PJVS) and a QHARS to provide a quantum measurement of a current (10 V/12.9kohm = 770 µA) that can be directly injected into a Kibble Balance operating in the range of 10 g to 200 g. The Kibble Balance provides mass dissemination traceable to the Planck constant while the robust quantum voltage, resistance, and current standards can be independently accessed for other electrical metrology needs.

Contact:
Darine Haddad
darine.haddad [at] nist.gov (darine[dot]haddad[at]nist[dot]gov)
301-975-6552

REFERENCES of Major Accomplishments:

“Flexure-Based Mechanism for a Kibble Balance”, L. Keck, PhD Thesis, 2025
https://doi.org/10.22032/dbt.63554

“Design of an enhanced mechanism for a new Kibble balance directly traceable to the quantum SI”, L. Keck et al, EPJ Techniques and Instrumentation, 9 :7, 2022
https://doi.org/10.1140/epjti/s40485-022-00080-3

“Magnet system for the Quantum Electro-Mechanical Metrology Suite”, R R Marangoni et al, IEEE Trans. Instrum. Meas., 69(8): 5736 – 5744, 2019
https://doi.org/10.1109/TIM.2019.2959852

KIBB-g2

Researchers in the PREME program have successfully demonstrated the first tabletop-sized Kibble balance operating in air at the gram level (KIBB-g1), achieving relative accuracies of a few parts in 10⁶. Building on the success of this prototype, PREME, through the NIST-on-a-Chip program, partnered with the Department of Defense to design and construct the next-generation tabletop Kibble balance (KIBB-g2), which was completed and deployed to Redstone Arsenal in 2024.

Tabletop Kibble balance team with second generation KIBB-g2 designed for commercialization capable of direct realization of masses ranging from [1 mg – 20 g] to OIML Class F1 accuracies.

Credit: NIST

KIBB-g2 represents an important step toward modernizing mass metrology by replacing traditional infrastructure that is labor-intensive, time-consuming, and vulnerable to damage during handling and shipping of physical artifacts. In contrast, Kibble balances offer a more robust, efficient, and SI-traceable approach.

The next phase of this partnership is already underway, focusing on the development and deployment of two additional tabletop Kibble balances to cover a dynamic range of [1 mg – 1 kg], targeting OIML F1 accuracy specifications. By merging mass and electrical metrology at primary metrology laboratories, this approach will streamline the entire traceability chain, enabling mass measurements to be directly linked to quantum-traceable electrical standards maintained in-house.

In parallel, PREME has also entered into a CRADA with a U.S. manufacturer to commercialize this technology. NIST currently owns and licenses two patents related to tabletop Kibble balance technology.

Contacts:
Leon Chao, Kumar Arumugam
leon.chao [at] nist.gov (leon[dot]chao[at]nist[dot]gov)
kumar.arumugam [at] nist.gov (kumar[dot]arumugam[at]nist[dot]gov)
301-975-4763

REFERENCES of Major Accomplishments:

L. Chao et al., “The design and development of a tabletop Kibble balance at NIST,” IEEE Transactions on Instrumentation and Measurement, 68(6):2176-2182, 2019

K. Arumugam et al., "Honey I Shrank the Kibble Balance: A Second Generation NIST Table Top Balance," 2024 Conference on Precision Electromagnetic Measurements (CPEM), Denver, CO, USA, 2024, pp. 1-2

L. Keck et al., “Thoughts on the Kibble–Robinson theory,” 2025 Metrologia 62 025012 DOI 10.1088/1681-7575/adc30e

US Patent US11187571B2, 2019

US Patent Pre-Grant Publication 2023/0375396

ENTR

ENTR_v2 on display at the DOD Maintenance Symposium in Salt Lake City, UT, 2024 directly calibrating a Snap-On torque screwdriver.

Credit: NIST

NIST is actively developing a new approach to directly realize electromagnetic torque using the Kibble principle. This self-calibrating tabletop instrument uses a free-spinning electromagnet to generate torque, enabling direct calibration of torque tools and eliminating the need for the traditional, complex traceability chains involving mass and length standards.

In collaboration with the U.S. Air Force Metrology Laboratory (AFMETCAL) and NIST-on-a-Chip (NOAC), two prototypes have been produced: ENTR_v1, a proof-of-concept instrument capable of calibrating torque tools from [1 mN·m – 20 mN·m] with 0.1% accuracy, and ENTR_v2, extending the range to [10 mN·m – 1 N·m], also achieving 0.1% accuracy. ENTR_v2 was field-deployed to Nellis Air Force Base, Nevada, in early 2025 and is currently undergoing operational testing by calibration maintainers.

Building on these successes, PREME researchers and AFMETCAL have begun the next phase: the design and development of ENTR3, a more powerful instrument expected to cover a range of [1 mN·m – 340 N·m] with 0.5% accuracy. This would cover approximately 95% of the torque calibrations typically encountered in DOD laboratories. (For comparison, a typical sports car generates about 300 N·m of torque at the wheels.)

In parallel, PREME has entered into a CRADA with Snap-On Industrial to commercialize this technology. NIST currently owns and licenses a patent related to the ENTR technology.

Contacts:
Leon Chao, Zane Comden, Chandra Shahi
leon.chao [at] nist.gov (leon[dot]chao[at]nist[dot]gov)
zane.comden [at] nist.gov (zane[dot]comden[at]nist[dot]gov)
chandra.shahi [at] nist.gov (chandra[dot]shahi[at]nist[dot]gov)
301-975-4763

REFERENCES of Major Accomplishments:

Z. Comden et al., "The Design and Performance of an Electronic Torque Standard Directly Traceable to the Revised SI," in IEEE Transactions on Instrumentation and Measurement, vol. 72, pp. 1-6, 2023, Art no. 1005506

2025 US Patent No. 12,276,559

Big G

The BIPM experiment being installed at NIST, Gaithersburg.

The universal constant of gravitation, G—often called “big G” to distinguish it from g, the acceleration due to Earth’s gravity—is one of nature’s fundamental constants. It quantifies the gravitational attraction between any two objects, whether they’re planets, people, or even office supplies. Yet despite centuries of effort, G remains the least precisely known of the fundamental constants. Its value is only known to five significant figures, and the range of experimental results differs by more than 20 times the uncertainty stated in the CODATA 2022 adjustment.

To address this longstanding challenge, NIST has taken a bold step: acquiring the experimental setups behind the two most significant outliers in G measurements—those from the International Bureau of Weights and Measures (BIPM) and JILA, a collaboration between the University of Colorado and NIST. Over the past five years, NIST researchers have conducted a new series of measurements using the BIPM torsion balance. The team is now analyzing the resulting data to determine a refined value of G, along with a robust uncertainty estimate, using this historic instrument.

Contact:
Stephan Schlamminger
stephan.schlamminger [at] nist.gov (stephan[dot]schlamminger[at]nist[dot]gov)
301-975-3609

REFERENCES of Major Accomplishments:

“Redetermination of the gravitational constant using the BIPM torsion balance”, S. Schlamminger, L. Chao, D.B. Newell, V. Lee, and C.C. Speake. In 2024 Conference on Precision Electromagnetic Measurements (CPEM), 2024
https://doi.org/10.1109/CPEM61406.2024.10646040

“Design of electrostatic feedback for an experiment to measure G”, S. Schlamminger, L. Chao, V. Lee, D. B. Newell, and C. C. Speake, IEEE Open Journal of Instrumentation and Measurement, 1:19, 2022,
https://doi.org/10.1109/OJIM.2022.3182391

“Closed form expressions for gravitational multipole moments of elementary solids, “J. Stirling and S. Schlamminger, Phys. Rev. D, 100:124053, 2019
https://doi.org/10.1103/PhysRevD.100.124053

Sixteen high-precision measurements of the gravitational constant (G) conducted over the past four decades, with the most recent results shown at the top. The vertical line marks the 2022 CODATA recommended value of G, while the gray band represents its one-standard-deviation uncertainty. The two red data points were obtained using the BIPM torsion balance, which is now located at NIST.

Credit: NIST

Quantum sensing for gravity

Chipscale torsion micropendulum. (a) Illustration (left) and photo (right) of a pendulum formed by suspending a 0.1 mg Si mass from a 75-nm-thick Si3N4 nanoribbon. (b) Energy ringdown revealing a quality factor of approximately 2 million. (c) Displacement spectrum of inverted (light blue) and normal (dark blue) device with frequency ω− = 2π ×20 Hz and ω+ = 2π ×32 Hz, respectively.

Credit: NIST

Gravimetry is essential for resource discovery, strategic defense, earth sciences, and realization and dissemination of the SI. Yet, despite the promise of better precision and accuracy using quantum sensing, gravimetry still relies on decades-old infrastructure. We seek to leverage NIST expertise in quantum sensing, artificial intelligence (AI), and nanofabrication to reshape the gravimetry infrastructure, aiming to solve problems ranging from GPS-denied navigation to the realization of the nation’s mass standards, to tabletop tests of the standard model of physics.

Absolute gravimetry is a critical element of NIST realization of mass. To align this measurement with emerging quantum technologies and the skills of a modern quantum engineering work force we have launched a new collaboration with researchers from the Fundamental Thermodynamics group, the Atomic Devices and Instrumentation group, and the high-Performance Computing and Visualization group, proposing a new approach to measure the local gravitational acceleration based on matter-wave interference. Absolute cold-atom gravimeters are presently limited by systematic effects that can be classified into two categories: those due to the transverse motion of the atoms through the interferometer (TM) and those due to the use of two different internal states in the interferometry sequence (IS). Our plan is to combine point source and Bragg atom interferometry modalities in a single quantum gravimeter, enabling us to characterize the wavefront on the one hand, and to exploit a single internal state on the other, thereby mitigating the primary sources of error limiting the accuracy of quantum gravimeters.

Relative gravimetry: Gravity must be known at the balance pan of all balances employing the Kibble principle. While micro-electro-mechanical systems (MEMS)-based relative gravimeters now operate at the state of the art, they are still too large for deployment on a tabletop Kibble balance and too expensive for deployment as gravity imagers, or as ubiquitous inertial sensors for autonomous vehicles. One obstacle is drift from temperature and aging that necessitates bulky, costly packaging and control. We are attacking this problem by sensing gravity the way it was in the time of Newton—using a pendulum clock. Quantum limited optical lever readout and piezo-actuated feedback control are being developed to create a mechanical Rayleigh/van der Pol Oscillator, whose clock frequency depends on gravity. Physically, the pendulum comprises a test mass the size of a grain of rice suspended from a taut nanoribbon that we create using NIST nanofabrication expertise. A laser then measures the gravitationally modulated oscillation frequency of the test mass for robust, compact detection.

Tabletop basic science: Several experiments have been proposed to answer fundamental questions concerning the nature of gravity and its potential as a quantum information channel. We are developing a variety of massive, highly coherent, torsion balances as part of a collaboration with the NIST/University of Maryland Joint Quantum Institute. Our work aims to explore the classical/quantum nature of gravitational coupling by placing a highly coherent torsion balance in proximity of various test masses, such as the atoms in an atom interferometer currently under development by the University of California Berkeley.

Contact:
Jon Pratt
Jon.pratt [at] nist.gov (Jon[dot]pratt[at]nist[dot]gov)
301-975-5470

REFERENCES of Major Accomplishments:

Nanoscale Torsional Dissipation Dilution for Quantum Experiments and Precision Measurement
J. R. Pratt, A. R. Agrawal, C. A. Condos, C. M. Pluchar, S. Schlamminger, and D. J. Wilson
Phys. Rev. X 13, 011018 – Published 15 February, 2023
DOI: https://doi.org/10.1103/PhysRevX.13.011018

Ultralow loss torsion micropendula for chipscale gravimetry
C. A. Condos, J. R. Pratt, J. Manley, A. R. Agrawal, S. Schlamminger, C. M. Pluchar, D. J. Wilson
arXiv:2411.04113

Microscale torsion resonators for short-range gravity experiments
J. Manley, C. A. Condos, S. Schlamminger, J. R. Pratt, D. J. Wilson, W. A. Terrano
Phys. Rev. D 110, 122005 – Published 20 December, 2024
DOI: https://doi.org/10.1103/PhysRevD.110.122005