What Is Quantum Metrology (and What It Is Not)

Quantum metrology uses fundamental properties of nature to realize measurement units. Instead of relying solely on physical artifacts or material-dependent standards, it links measurements to fundamental constants such as the Planck constant, the elementary charge, and the Boltzmann constant.

In this context, quantum metrology refers specifically to the realization of SI units from fixed fundamental constants, not to quantum-enhanced sensing research such as entanglement-based measurement techniques.

These constants are invariant. They do not drift over time, degrade with use, or depend on environmental conditions. This makes them ideal foundations for defining SI units.

This should not be confused with quantum computing or the routine use of experimental quantum sensors in commercial calibration laboratories. It is important to be clear about what this does not mean. Most commercial calibration laboratories do not operate quantum experiments or primary quantum standards. Instead, quantum metrology is applied at the highest levels of the traceability chain, primarily within national metrology institutes and a limited number of specialized laboratories. For a broader explanation of how quantum metrology fits within the SI system and what it does not encompass, see our overview.

Customers benefit indirectly. The advantages of quantum metrology flow downstream through improved traceability and more stable uncertainty foundations.

Key Takeaways: Understanding Quantum Metrology and SI Traceability

• Quantum metrology anchors measurement units to fundamental constants.
  Constants such as the Planck constant, Boltzmann constant, and elementary charge provide invariant references for defining SI units.
• Most calibration customers benefit indirectly.
  Quantum realizations occur primarily at national metrology institutes. Commercial calibration laboratories disseminate traceability from these stabilized upstream references.
• Traceability chains affect measurement uncertainty.
  Each step in a traceability chain adds uncertainty. Quantum-based realizations can reduce uncertainty growth at the highest levels.
• Electrical calibration demonstrates real-world application.
  Voltage and resistance standards based on the Josephson effect and quantum Hall effect are widely used in high-accuracy electrical metrology.
• Traceability should reference the SI, not a specific organization.
  Calibration certificates should state traceability to the International System of Units (SI), aligning with ISO and ILAC guidance.
• Accreditation frameworks remain central.
  ISO/IEC 17025 and ANSI/NCSL Z540 measurement assurance requirements continue to govern competence and uncertainty evaluation.

Why Traceability Chains Matter to Calibration Customers

Every calibration result depends on a traceability chain that links the measurement back to the SI. In practice, this chain includes multiple reference standards, calibration steps, and transfers.

Each step in the chain adds uncertainty. Even when each step is well controlled and fully compliant with ISO/IEC 17025, uncertainty accumulates as measurements are disseminated from primary references to working instruments.

In some cases, quantum-based realizations allow SI units to be realized directly from fundamental constants rather than transferred from physical artifacts. When this occurs, a step in the traceability chain may be eliminated or stabilized.

For customers operating near specification limits, being closer to the SI can materially reduce uncertainty growth. This lowers the risk of false accept (consumer risk) or false reject (producer risk) decisions, improving confidence in compliance, yield, and long-term product quality.

The SI Redefinition and Its Practical Impact

In 2019, the International System of Units was redefined so that several base units are now defined by fixed numerical values of fundamental constants. These include the kilogram, ampere, kelvin, and mole.

As a result, national metrology institutes now realize these units using quantum-based experiments rather than relying on unique physical artifacts.

For calibration customers, this did not require changes to calibration procedures or certificates. What changed is the stability and reproducibility at the top of the traceability chain. The SI is now realized in a way that is more robust, more universal, and less vulnerable to drift or artifact degradation.

From a calibration standpoint, this strengthens traceability to the SI and supports more defensible uncertainty budgets downstream, particularly for long-term or high-accuracy measurements.

Electrical Calibration: A Practical Example

Electrical calibration provides the most mature example of quantum metrology in routine use. We explore this application in greater detail in our discussion of quantum metrology calibration.

Voltage is realized using Josephson junctions, which link voltage directly to frequency and the Planck constant. Resistance is realized using the quantum Hall effect, providing exceptionally stable and reproducible resistance values.

Most calibration laboratories do not operate primary Josephson or quantum Hall systems. Instead, they rely on calibrated reference standards that are traceable to these quantum realizations through national metrology institutes or accredited reference laboratories.

For customers, the practical benefit is stability. Drift-related uncertainty components are reduced, long-term consistency improves, and confidence in high-accuracy voltage and resistance calibrations increases.

Benefits Beyond Reduced Measurement Uncertainty

Reduced uncertainty accumulation is a primary benefit, but it is not the only one.

• Long-term consistency: Quantum-based realizations do not depend on material stability, supporting better trending and historical analysis.
• Global equivalence: Measurements based on fundamental constants are inherently comparable across countries, reducing risk in global manufacturing and supplier qualification.
• Reduced artifact dependence: Reliance on unique physical artifacts is minimized, lowering exposure to loss, damage, or undetected drift.
• Clearer traceability explanations: Traceability paths that terminate in quantum-based SI realizations are easier to defend during audits and regulatory reviews.

Traceability to the SI, Not to an Organization

Quantum metrology reinforces an important distinction in calibration documentation.

Traceability statements should reference traceability to the SI, not to a specific national metrology institute such as NIST. National institutes realize and disseminate SI units, but they are not the definition of those units.

As SI units are increasingly realized directly from fundamental constants, traceability becomes more explicitly tied to the SI itself rather than to any individual organization. This aligns with ILAC and ISO guidance and supports international recognition of calibration results.

Standards, Accreditation, and Measurement Assurance

Quantum metrology fits fully within existing accreditation frameworks. ISO/IEC 17025 requirements for traceability, uncertainty evaluation, and technical competence remain unchanged.

The ANSI/NCSL Z540 series continues to emphasize measurement assurance, risk-based decision-making, and fitness for intended use. Quantum metrology does not replace these principles. It strengthens the technical foundation on which they are applied.

Most calibration laboratories will continue to disseminate units using calibrated reference standards rather than direct quantum realizations. What improves is the stability and quality of the upstream references supporting those standards.

What This Means for Calibration Customers

Customers do not need quantum standards in their laboratories to benefit from quantum metrology. The value is realized through stronger traceability to the SI, better uncertainty control, and reduced long-term measurement risk.

For customers, this means:

• More defensible calibration decisions
• Lower risk near specification limits
• Greater confidence in audits and regulatory reviews

In industries where calibration affects safety, quality, or compliance, these improvements directly support better outcomes.

Final Perspective

Quantum metrology does not replace traditional calibration practices. It strengthens the foundation beneath them. By anchoring SI units to invariant fundamental constants, it improves long-term stability at the top of the traceability chain and supports more consistent uncertainty evaluation downstream.

For calibration customers, the practical impact is clearer traceability to the SI, stronger confidence in measurement results, and reduced decision risk, especially when operating near specification limits. In industries where compliance, safety, and product quality depend on defensible measurements, a stronger foundation translates directly into better outcomes.

If you want to better understand how your calibration program connects to the modern SI, and how your traceability chain and uncertainty budgets support defensible decisions, speak with SIMCO about strengthening traceability, managing uncertainty risk, and improving audit confidence.

 

FAQ

What does quantum metrology mean in simple terms?
Quantum metrology uses fundamental physical constants to define measurement units instead of relying solely on physical artifacts. Because these constants do not change, they provide a stable foundation for the SI.

Does quantum metrology mean labs now use quantum experiments?
No. Primary quantum standards are typically operated by national metrology institutes. Most ISO/IEC 17025 accredited labs rely on calibrated reference standards that are traceable to those realizations.

How does quantum metrology improve calibration traceability?
By tying SI units to invariant constants, quantum metrology strengthens the top of the traceability chain. This reduces long-term instability and supports more defensible uncertainty budgets.

What are examples of quantum standards used in electrical calibration?
Josephson voltage standards and quantum Hall resistance standards are the most established examples. These systems link electrical measurements directly to fundamental constants.

Does quantum metrology reduce the need for calibration intervals?
No. Calibration intervals and measurement assurance programs remain essential. Quantum metrology improves upstream stability but does not eliminate routine calibration requirements.

Why does this matter for compliance and audits?
Stronger traceability to the SI supports international recognition, audit defensibility, and confidence in measurement decisions, particularly in regulated or high-risk industries.

 

Related Reading: 

Metrology vs. Calibration Explained – Clarifies the distinction between metrology and calibration, and explains how each contributes to traceability, uncertainty control, and measurement assurance.

Calibration Lab Best Practices – Outlines the operational and quality controls that support ISO/IEC 17025 compliance, defensible uncertainty statements, and consistent calibration performance.

Boost Precision With SIMCO Calibration Services – Describes how structured calibration programs strengthen traceability chains, reduce uncertainty risk, and support audit confidence.

Explore More Calibration & Metrology Insights – Provides additional technical perspectives on SI traceability, accreditation frameworks, and practical calibration strategy.