American researchers from the National Institute of Standards and Technology (NIST) have just produced a little gem: they recently announced the commissioning of the most precise atomic clock ever built.
These are the most advanced timekeeping instruments in the world, so much so that they have radically changed the face of our civilization. The time provided by atomic clocks is today the basis of all modern communication and navigation systems. We can also cite the world of financewhich relies on extremely precise timestamps to guarantee the authenticity of transactions on different markets, or l’infrastructure web, which requires near-perfect synchronization to maintain data integrity and security. The same is true for the Scientific Researchespecially in fundamental physics; without this ability to measure time very precisely, humanity would have been deprived of many very important discoveries.
In all these cases, good old quartz watches are no longer suitable. To achieve such precision, scientists have therefore chosen to rely on the quantum properties of matter at the smallest of scales.
The quantum dance of atoms in the service of measuring time
The nuclei of some atoms are constantly rotating on themselves, which gives them magnetic properties. At the same time, they are surrounded by electrons distributed in different “orbits” that correspond to different energy levels. They too have magnetic properties. The interactions between these two magnetic systems give rise to a somewhat unusual phenomenon: the atom can exist at two distinct energy levels, with a tiny but nevertheless measurable difference between the two. This is called the hyperfine structure.
When the atom is bombarded with perfectly calibrated electromagnetic waves, the atom begins to alternate between the two energy levels at a very high and, above all, incredibly precise rate. For example, cesium-133, which is used in many atomic clocks, vibrates very precisely 9,192,631,770 times per second when flooded with microwaves.
It is this exceptional regularity that is used to time events with breathtaking precision. A cesium-133 clock, for example, loses about one second every 315 million years. For reference, a typical quartz watch typically loses a second every few days.
A new generation of optical atomic clocks
But as science and technology advance, so do the demands for precision. Incredibly, even cesium atomic clocks are starting to show their limitations in some cases, particularly when it comes to testing the limits of the models that underpin our understanding of the Universe. So specialists are working on a new generation optical atomic clocks. This is the category to which the new NIST creation belongs.
Unlike older models, these devices rely on visible light, which has a much higher frequency than microwaves. This allows the atoms in question to be examined more times per second. But to take advantage of this higher frequency, atoms that change energy levels at a higher rate must also be found.
Some of these clocks are based on elements like ytterbium or strontium, which vibrate several hundred billion times per second. It is the latter that American physicists used to design their new clock.
They trapped a few tens of thousands of strontium atoms in a mesh of laser beams. This high number and this electromagnetic trap make it possible to statistically eliminate possible measurement errors. We therefore end up with a system of incredible precision. According to its designers, this optical atomic clock with strontium would only loseone second every… 30 billion years — more than twice the age of the Universe ! A very exciting prospect for the entire scientific community.
Implications for navigation and quantum computing…
For starters, this precision could revolutionize disciplines likeastronautics. In this field, a seemingly negligible error can mean the difference between arriving within range of the target planet… or missing it by hundreds of thousands of kilometers, and thus drifting towards the edge of space. With such a reliable timer, it will be possible to plan extremely complex and precise trajectories to push the boundaries of space exploration.
Indirectly, optical atomic clocks could also pave the way forHuge progress in quantum computing. To function, quantum computers need to maintain qubits in a state of coherence. This means that they must be able to remain in a stable quantum superposition state while remaining entangled with each other for a certain time.
Maintaining this coherence is one of the biggest challenges facing quantum computing scientists today. These overlapping, entangled sets of qbits are incredibly delicate systems, and the slightest disturbance can cause this fragile harmony to collapse. But the laser mesh that holds the strontium atoms in place in an optical atomic clock could also lock the qbits together, paving the way for more powerful and stable quantum computers, the researchers say.
…and a step towards the Theory of Everything
But probably the most interesting implications are those that concern fundamental physics.
Today, specialists rely on two major paradigms to describe how our world works: general relativity and the quantum physicsformalized in what is called the Standard Model of particle physics. These two theories describe extremely well the phenomena that we observe in practice, respectively at the largest and smallest scales. They therefore serve as the basis for a large part of our science.
Both work extremely well on their own. In recent years, several studies have further demonstrated the immense robustness of general relativity, and quantum physics continues to advance at great speed. The problem is thatthey remain completely irreconcilable at the present time..
The most eloquent example is that of the gravitationGeneral relativity states that it is generated by deformations of space-time; the more intense it is, the slower time passes. On the other hand, there is absolutely nothing in the standard model that can explain this phenomenon so well described by Einstein.
We then find ourselves in a dead end that is both terrifying and exciting, because it strongly suggests that we are missing at least one crucial element to arrive at the famous “ Theory of Everything » — a unified model capable of describing all fundamental forces from a single theoretical foundation. This theory was Einstein’s ultimate goal, and a whole section of theoretical physics is still trying to build this bridge between quantum physics and relativity.
Unfortunately, these phenomena are very difficult to study rigorously on our scale. For example, until now, physicists did not have no instruments powerful enough to precisely quantify the relativistic effects described by Einstein on a small scale. But that could change with this new generation of optical atomic clocks.
According to the authors of this work, they are able to detect them on a scale of less than a millimeter. Moving the clock by a distance equivalent to the thickness of a hair is already enough to detect the tiny fluctuations in time caused by gravity. Therefore, these instruments could finally help us identify breaking points in our understanding of the fundamental forces of nature. With potentially enormous implications for all of modern science.
« We are pushing the limits of time measurement “, summarizes Jun Ye, a physicist at NIST and co-author of the associated study. We’re exploring the frontiers of measurement science, and when we can quantify things with this level of precision, we start to see things that we could only theorize about until now. “, he rejoices. It will probably take years to get there, but this breakthrough at the frontiers of physics already promises to lead to absolutely fascinating results.
The text of the study is available here.
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