Metrology: The fabric of science and technology Lafe Spietz TMA class of 1990

What is metrology? The science of measurement (not weather!) Metrology establishes the international standards for measurement used by all countries in the world in both science and industry Examples: distance, time, mass, temperature, voltage, values of physical and chemical constants

Why is metrology important and interesting? Standard units and values of constants needed for all science Technological standards make all technology work better and can save lives: fire hydrant standards Measurement of constants can give fundamental insights into the universe: drift of fine structure constant

Who does metrology? “The Congress shall have Power To… …fix the Standard of Weights and Measures;” From Article I, section 8 of the U.S Constitution: Government labs around the world.

SI: The International System of Units Length: meter (m) Mass: kilogram (kg) Time: second (s) Electric current: ampere (A) Thermodynamic temperature: kelvin (K) Amount of substance: mole (mol) Luminous intensity: candela (cd) Seven base units: Lots of derived units: Area: m 2 Speed: m/s Force: 1 newton = 1 kg·m/s 2 Voltage: 1 volt = 1 m 2 ·kg/s 3 ·A Frequency: 1 hertz = 1/s Power: 1 watt = 1 kg·m 2 /s 3 Electric Charge: 1 C = 1 A·s

Hierarchy of units: Kings and queens of units: Time, frequency, distance Dukes and Earls: Current, voltage, resistance Peasants: Mass, temperature, pressure, luminosity

Clocks: Atomic time One part per quadrillion accuracy!!! Accurate frequency gives accurate distance and time.

Artifact vs. quantum standards: A metal bar: The meter is the length of the path traveled by light in vacuum during a time interval of 1/299,792,458 of a second The modern meter:

The story of mass I: the modern kilogram The SI kilogram drifts!

The story of mass II: possible replacements Watt-balance Avogadro’s number Measurement: Roundest object in the world! Goal: 10 parts per billion accuracy

Temperature: Kelvin, Celsius, and Fahrenheit 294 K 70 F21 C K32 F0 C 77 K-321 F-196 C 4.2 K-452 F-269 C 0 K F C Water freezes Air liquefies Helium liquefies Room temperature Absolute zero

The kelvin: the SI unit The kelvin, unit of thermodynamic temperature, is the fraction 1/ of the thermodynamic temperature of the triple point of water. (0.006 atm)

ITS-90: the practical realization of the kelvin Platinum resistance standard Constant volume gas thermometer PV=Nk B T Not primary!!!

PLTS-2000: the low temperature definition of the kelvin Superconducting fixed points Helium-3 melting pressure thermometer Not primary, and very hard!!

Electrical noise and temperature: The basic idea All resistors make electrical noise proportional to temperature: hissing of a radio

Electrical noise and temperature: applications of noise thermometry By measuring the electrical noise of antennas pointed towards space, astronomers can measure the background temperature of the universe! (images courtesy ofNASA/WMAP Science Team)

Why noise thermometry is hard: Amplifiers add noise, and have complex behavior Must be calibrated accurately to measure temperature accurately

The Shot Noise Thermometer V P { Relates temperature to voltage, Simplifying amplifier calibration.

The Shot Noise Thermometer: Total cost of package <10$ Tunnel Junction Built-in Bias Tee (on-board SMT Components) Copper Plumbing parts SMA Connectors for RF Copper Tubing for DC lines A new practical low temperature thermometer