Why simple tasks like charging your phone rely on quantum measurements

In today’s fast-paced digital world, if you resemble many smartphone users, your device is frequently in need of charging. However, the safety of this everyday task hinges on intricate quantum measurements originating from cutting-edge physics.

To fully grasp this concept, we must explore what transpires when a charger is connected to a power outlet. The electricity streaming from a wall socket can exceed one hundred volts. Yet, through sophisticated engineering, chargers reduce this to a mere dozen volts, preventing a potential disaster that could leave your device in flames.

This emphasizes the critical importance of precise voltage measurements. But how do we ascertain what constitutes a single volt? Who is responsible for ensuring that the voltage specifications on your phone charger are accurate?

This question transcends mere scientific theory. In the US, the legal definition of a volt has been in place since 1904 and is upheld by the National Institute of Standards and Technology (NIST). This agency ensures uniformity across industries regarding core measurement units – whether they be volts, kilograms, or seconds. Numerous other nations, including the UK with its National Physical Laboratory, maintain similar metrology units.

Interestingly, for over three decades, NIST has defined the volt through a quantum device. Metrologists utilize a series of superconducting junctions, comprised of multiple narrow superconducting regions separated by insulating material, which are subjected to microwaves of a precise frequency. This interaction induces a voltage difference between the junctions directly correlated to two fundamental constants of the universe, allowing researchers to use universal numbers to establish the definition of a volt.

The two pivotal constants here are the charge of an electron and Planck’s constant, which links the energy of a photon (light particle) to its frequency. Thus, the connection between charging your device and the fundamental aspects of the quantum world is quite direct.

The volt isn’t an isolated case; many other units have undergone similar transformations into the realm of quantum measurements. In 2018, global metrologists voted to redefine several SI units in ways that anchor them more closely to the microscopic world.

For example, consider the kilogram. It transitioned from being represented by a heavy platinum alloy to being defined by a combination of Planck’s constant, the speed of light, and the frequencies related to electronic transitions in atomic clocks. Thus, if you recently used a scale at your doctor’s office, quantum physics played a role in determining that number.

This shift toward quantum-based definitions mirrors substantial scientific progress made over the past few decades in understanding and manipulating our universe’s building blocks at their smallest scales. For instance, in January, I interviewed Alexander Aeppli from the University of Colorado Boulder, a key player in developing some of the most precise clocks globally. He mentioned, “Frequency is the best thing humans have ever measured; we’re experts at measuring frequency.” In this context, frequency measurement captures the rapid energy transitions of electrons within atoms, dictated by the laws of quantum mechanics.

This exceptional level of control over quantum systems benefits not only the precise definitions of time but also opens potential applications for atomic clocks in calculating the shape of Earth or developing advanced early warning systems for natural disasters.

The quantum revolution in measurement standards also aims to make the world’s best tools more accessible. Before the 2018 redefinitions, manufacturers and researchers needed to send devices to local metrology institutes for calibration and certification. However, current standards are based on natural constants, available to anyone with a sufficiently equipped lab. “The goal is to make ourselves obsolete,” remarks Richard Davis, a retired figure from the International Bureau of Weights and Measures. “The entire system is far more flexible and less Eurocentric.”

“With all this equipment, people indeed continue to come to us. However, post-redefinition, our mission has shifted towards empowering others to perform their own measurements,” notes NIST’s Jason Underwood during our August discussion. “Now under the new SI framework, we’re focused on creating instruments that provide traceability to those fundamental constants.”

Recently, Underwood and colleagues unveiled a prototype of a quantum device capable of measuring three different electrical units, including volts, simultaneously. This device, if portable, could significantly simplify and reduce costs for businesses needing certification against relevant standards.

Historically, the evolution of measurement units has increasingly leaned towards quantum explanations, yet the future of these electrical units remains uncertain. For instance, the quantum standard for electrical measurements hasn’t been universally recognized like measurements of the second or kilogram, necessitating further experimentation for validation. Similar advancements are also underway globally through initiatives like the EU-based QuAHMET consortium.

The definition of the second is also under consideration, as researchers aim to develop improved atomic clocks that could redefine how we perceive time measurement. In April, I followed an international research team’s journey to compare advanced atomic clocks from Japan, the UK, and Germany, a mission still ongoing; expect more updates on quantum clocks in future reports.

Despite metrologists’ efforts for stability in their definitions, the work itself remains contingent upon national funding and international relationships. This has always been a challenge since metrology’s inception; during the first international convention on measurements in 1875, political tensions between France and Germany impacted discussions. Presently, discussions around NIST’s infrastructure highlight similar concerns; a 2023 study revealed the agency’s infrastructure deteriorating. Earlier this year, the Trump administration proposed a drastic budget cut to NIST, highlighting the intertwining of metrology work with national politics, although Congress ultimately rejected that proposal.