What Makes Rolex Great? Part-III

Part Three - Defining Time With The Rubidium Optical Atomic Clock

For Rolex, keeping time precisely is important. But what’s monumental is defining it.

In May 2025, Rolex did something almost no luxury watchmaker has ever attempted: it stepped beyond making watches and into defining the second itself. By establishing Rolex Quantum SA - a new entity in Neuchâtel dedicated to optical atomic timekeeping, Rolex moved from being a user of precision to a producer of the reference that underpins it.

At the heart of this ambition is the Rolex Rubidium Optical Atomic Clock, a device the brand says is up to 60 times more accurate than conventional atomic clocks and now helps generate the “superlative second” used to calibrate Rolex’s own precision-testing machines.

How Rolex defines time

For Rolex, the answer to the above is no longer rhetorical. The company now uses its Rubidium Optical Atomic Clock to help produce the very second that sets the benchmark for its Superlative Chronometer certification - the internal standard that guarantees each watch a precision of −2/+2 seconds per day. In practical terms, that means the oscillators inside Rolex’s timing rigs are no longer referenced only to external time signals, they are disciplined by a second derived from Rolex’s own optical clock.

This is more than a marketing flourish. Three units of the clock have been built: two installed at Rolex sites in Geneva and Bienne as master references for the brand’s internal time scales, and a third at METAS (the Swiss Federal Institute of Metrology) in Wabern. Signals from all three are transmitted to the International Bureau of Weights and Measures (BIPM) in Paris, where data from roughly 450 atomic clocks worldwide are combined to realize Coordinated Universal Time (UTC). In other words, Rolex now helps set the time by which the world synchronizes navigation, telecoms, and financial systems - and by which its own watches are judged.

What actually is a second? From earth’s spin to the atom

For most of history, a second was a fraction of a day: 1/60 of a minute, 1/3,600 of an hour, 1/ 86,400 of a day - where “day” meant one rotation of the Earth. The problem is that Earth is not a perfect metronome. Its rotation slows over geological time and wobbles on shorter scales, so a second defined as 1/86,400 of a day is not truly constant.

To solve this, the second was redefined in 1967 in terms of something far more invariant: the radiation emitted by a specific atomic transition. The SI definition reads: a second is “the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium-133 atom.” That number was chosen for backward compatibility with the astronomical second (essentially the length of the year 1900), but the definition itself is now purely atomic. In contrast, a quartz oscillator vibrates about 32,768 times per second.

Conventional atomic clocks probe a beam of caesium-133 atoms with microwaves near 9.2 GHz and count those cycles to realize the second. These clocks are astonishingly stable - modern caesium standards will not lose a second in hundreds of millions of years - but they are no longer the frontier.

Atomic clocks, optical clocks, and why frequency matters

The accuracy of an atomic clock improves with the frequency of the “ticks” it counts. Caesium clocks operate in the microwave domain (~9.2 GHz). Optical atomic clocks, by contrast, use transitions in the hundreds of terahertz - roughly 100,000 times higher. They are capable of subdividing a single second into 750 quadrillions. Each of these tiny segments of time represents approximately one femtosecond. Thus, by counting the oscillations of light from these optical atomic clocks, one can be certain of the time to within a femtosecond. More ticks per second means finer resolution and, all else being equal, lower fractional uncertainty.

National labs such as the UK’s NPL now pursue optical clocks based on strontium and ytterbium with fractional uncertainties approaching 1 part in 10¹⁸, about two orders of magnitude better than primary caesium standards. The long-term plan in metrology circles is to eventually redefine the SI second on an optical transition, once the technology and international comparisons mature.

Rolex’s move sits precisely at this inflection point: taking optical-clock performance out of pure research and into an industrial-grade time-scale system that runs 24/7 and feeds directly into UTC.

The Rolex Rubidium Optical Atomic Clock: architecture and performance

Rolex’s device, according to the patent application WO2025233363A1, is described as a “Two-Photon Rubidium Optical Atomic Clock,” developed with the Swiss Centre for Electronics and Microtechnology (CSEM) in Neuchâtel. Its physics is elegant: rubidium atoms are heated into a gas, then laser-cooled and stabilized to within a thousandth of a degree. An erbium-doped optical fiber amplifies laser light that excites the rubidium at a very precise, very high frequency - about 385 terahertz. When the excited atoms decay back to their ground state, they emit a characteristic blue fluorescence. That fluorescence signal is the clock’s “pendulum”: its phase and frequency are locked to the atomic resonance, and that locked optical frequency becomes the reference from which the second is derived.

Why rubidium? In this configuration, rubidium offers a combination of stability and practicality that suits an industrial master clock. Rolex and CSEM have presented work showing rubidium-based optical systems that are even more stable than caesium references in continuous operation. Prototype devices tested as master clocks at Rolex’s Geneva and Bienne sites reportedly deviated by less than 300 picoseconds after one week - on the order of a few parts in 10¹⁴ over that interval - demonstrating the kind of drift performance needed for a national time-scale contributor.

Rolex states that its optical clock’s accuracy surpasses other atomic clocks by as much as 60 times, with operational stability unmatched for a clock of this type. Its drift is specified at less than 0.1 billionth of a second per day - equivalent to less than one second per million years. Put differently: if you ran this clock continuously for a million years, it would still be within a second of the ideal atomic second.

According to Rolex, “In an industrial, calibrated version, the clock provides the most accurate second - doing so continuously and with the greatest of regularity.”

Why this is better than a “regular” atomic clock

Three factors make the Rolex Rubidium Optical Atomic Clock superior to conventional caesium clocks for its intended role:

-  Higher oscillation frequency: Operating at ~385 THz instead of ~9.2 GHz gives roughly 40,000× more cycles per second to average over, reducing statistical noise and improving short- and medium-term stability.

-  Optical interrogation and two-photon excitation: The two-photon scheme reduces certain systematic shifts and broadening effects that limit microwave clocks, tightening the lock between the laser and the atomic resonance.

-  Industrialized stability: The clock is engineered not as a one-off lab demonstrator but as a continuously running master oscillator integrated into redundant time scales at two Rolex sites and at METAS. That redundancy and continuous operation are crucial for contributing meaningfully to UTC.

The Rolex Rubidium Optical Atomic Clock is smaller and requires less power than many laboratory-grade atomic clocks, making it more practical for deployment outside controlled research environments. Each unit is compact for its category at approximately 19 in (or about 48 cm) in height and has been engineered for perpetual operation.

The result is a timebase that is not only more accurate in the abstract but more useful in practice: it can discipline other clocks, synchronize instruments, and serve as a reference for high-precision testing without frequent recalibration.

From lab prototype to global time infrastructure

Rolex Quantum SA formalizes what began as an R&D collaboration. Incorporated in May 2025 and based steps from the historic Neuchâtel Observatory, the company is chaired by Rolex CEO Jean-Frédéric Dufour and led operationally by engineer Fabien Droz, a former leader in instrumentation at CSEM. The location is deliberate: Neuchâtel has been a cradle of Swiss chronometry since the era of Abraham-Louis Breguet and the observatory trials that defined precision watchmaking.

According to Oliver Greim - Head of Research and Development at Rolex, “Precision is our heritage and our future. With Rolex Quantum, enabled by CSEM’s technology transfer, we are building clocks that serve our own timing systems and help keep the world on time.”

The technology transfer from CSEM to Rolex Quantum converts research prototypes into production-ready optical clocks for industrial and metrological use. These are not wristwatch components - they are infrastructure. Applications include satellite navigation (GPS, Galileo), telecom network synchronization, and national time scales that feed UTC. By placing one clock at METAS, Rolex ensures its optical ticks enter the Swiss national timekeeping chain and onward to the International Bureau of Weights and Measures (BIPM) in Paris, where they help realize the world’s civil time.

Impressively, the Rolex Rubidium Atomic Optical Clock is the first atomic optical clock to contribute to Coordinated Universal Time.

A quantum leap

Rolex’s relatively conservative watch design evolution and the absence of high complications in its portfolio sometimes gets called for lack of “innovation”. However, in reality, Rolex is perpetually invested in making staggering technical breakthroughs.

Rolex’s Rubidium Optical Atomic Clock signifies the above and shifts the company’s relationship with precision from passive to active. With rubidium atomic clocks predicted as replacements for the caesium-133 microwave models, which have defined the second since 1967, Rolex’s invention with hundred times more precision could well be used to calculate International Atomic Time (TAI). In the future, in addition to offering the most precise watches in the world, Rolex could contribute to redefining the second, the unit of time in the International System of Units, and who knows, perhaps it would also rewrite the standards of chronometry in the process, by combining precision mechanical calibers and a time reference at the atomic scale.

The second, redefined

A second began as a slice of a day, became a count of caesium cycles, and is now being recast in optical light. Rolex’s Rubidium Optical Atomic Clock stands at the leading edge of that transition: a device that turns the blue fluorescence of excited rubidium atoms into the reference by which watches - and, increasingly, the world - are timed. In building Rolex Quantum and deploying these clocks into the Swiss and global time ecosystem, the company has done more than improve its own accuracy. Rolex has inserted itself into the very definition of time, making it even greater.

You can find the other parts of the What Makes Rolex Great? series here: Part-1 and Part-II.