A study by MIT has found that the stability of clocks, lasers, and other oscillators is not only affected by environmental noise but also by quantum mechanical effects. The researchers, including Vivishek Sudhir, assistant professor of mechanical engineering at MIT, and Hudson Loughlin, a graduate student in MIT’s Department of Physics, suggest that by manipulating the states that contribute to quantum noise, the stability of an oscillator could be improved beyond its quantum limit. This could lead to super-quantum precision in timekeeping, potentially advancing technologies such as satellite communications, GPS systems, and quantum computing.
Quantum Limitations on Timekeeping Precision
The stability of timekeeping devices, such as clocks and lasers, is influenced by the noise in their environment. For instance, a slight wind can disrupt a pendulum’s swing, and heat can interfere with the oscillations of atoms in an atomic clock. While eliminating environmental effects can enhance a clock’s precision, it can only do so to a certain extent. A recent study by MIT researchers has found that even if all external noise is removed, the stability of these devices would still be susceptible to quantum mechanical effects, limiting their precision.
The researchers have also proposed a theoretical solution to surpass this quantum limit. By manipulating or “squeezing” the states that contribute to quantum noise, the stability of an oscillator could be improved beyond its quantum limit. This discovery suggests that there is a limit to the stability of oscillators like lasers and clocks, which is not only set by their environment but also by quantum mechanics. However, this quantum mechanical shaking can be overcome by manipulating the quantum states themselves.
The team is currently working on an experimental test of their theory. If successful, they envision that clocks, lasers, and other oscillators could be tuned to super-quantum precision. These systems could then be used to track infinitesimally small differences in time, such as the fluctuations of a single qubit in a quantum computer or the presence of a dark matter particle flitting between detectors.
Quantum Noise and Laser Precision
In their study, the researchers first examined the stability of lasers, which are optical oscillators that produce a wave-like beam of highly synchronised photons. They found that a laser’s stability is limited by quantum noise. This conclusion supports a hypothesis put forth by physicists Arthur Schawlow and Charles Townes, who are largely credited with the invention of the laser.
Previous studies have tested this hypothesis by modelling the microscopic features of a laser. Through specific calculations, they showed that imperceptible, quantum interactions among the laser’s photons and atoms could limit the stability of their oscillations. However, these studies were based on extremely detailed, delicate calculations, and the limit was only understood for a specific kind of laser.
Simplifying the Quantum Noise Problem
The MIT team sought to simplify the problem by focusing on the abstract picture of all oscillators, rather than the physical intricacies of a laser. They drew up a simplified representation of a laser-like oscillator, consisting of an amplifier, a delay line, and a coupler. They then wrote down the equations of physics that describe the system’s behaviour and carried out calculations to identify where quantum noise would arise in the system.
The team found that quantum fluctuations come into the system in two places: the amplifier and the coupler. Knowing these two things allows us to understand the quantum limit on that oscillator’s stability. The researchers believe that scientists can use the equations they lay out in their study to calculate the quantum limit in their own oscillators.
Overcoming the Quantum Limit with Quantum Squeezing
The team also discovered that the quantum limit might be overcome if quantum noise in one of the two sources could be “squeezed”. Quantum squeezing is the concept of minimising quantum fluctuations in one aspect of a system while proportionally increasing fluctuations in another aspect. In the case of a laser, if quantum fluctuations in the coupler were squeezed, it could improve the precision of the outgoing laser beam, even as noise in the laser’s power would increase as a result.
This finding suggests that quantum mechanical limits are not absolute and can be manipulated to some extent. This result is applicable to a wide class of oscillators, opening up new possibilities for enhancing the precision of timekeeping devices.
Future Implications and Developments
The researchers plan to demonstrate several instances of lasers with quantum-enhanced timekeeping ability over the next few years. They hope that their recent theoretical developments and upcoming experiments will advance our fundamental ability to keep time accurately and enable new revolutionary technologies.
The team’s work, detailed in an open-access paper published in the journal Nature Communications, has the potential to significantly impact the field of quantum computing. If they can demonstrate that they can manipulate the quantum states in an oscillating system, it could lead to the development of clocks, lasers, and other oscillators with super-quantum precision. These systems could then be used to track infinitesimally small differences in time, such as the fluctuations of a single qubit in a quantum computer or the presence of a dark matter particle flitting between detectors.
“What we’ve shown is, there’s actually a limit to how stable oscillators like lasers and clocks can be, that’s set not just by their environment, but by the fact that quantum mechanics forces them to shake around a little bit,” says Vivishek Sudhir, assistant professor of mechanical engineering at MIT. “Then, we’ve shown that there are ways you can even get around this quantum mechanical shaking. But you have to be more clever than just isolating the thing from its environment. You have to play with the quantum states themselves.”
“We plan to demonstrate several instances of lasers with quantum-enhanced timekeeping ability over the next several years,” says Hudson Loughlin, a graduate student in MIT’s Department of Physics. “We hope that our recent theoretical developments and upcoming experiments will advance our fundamental ability to keep time accurately, and enable new revolutionary technologies.”
“When you find some quantum mechanical limit, there’s always some question of how malleable is that limit?” Sudhir says. “Is it really a hard stop, or is there still some juice you can extract by manipulating some quantum mechanics? In this case, we find that there is, which is a result that is applicable to a huge class of oscillators.”
Quick Summary
An MIT study has found that the stability of clocks, lasers, and other oscillators, even when all external noise is eliminated, is still susceptible to quantum mechanical effects, limiting their precision. However, the researchers also demonstrated that by manipulating the states contributing to quantum noise, the stability of an oscillator could be improved, potentially allowing for super-quantum precision in timekeeping and other applications.
- A study by MIT has found that the stability of clocks, lasers, and other oscillators is not only affected by environmental noise but also by quantum mechanical effects.
- The researchers, including Vivishek Sudhir, assistant professor of mechanical engineering at MIT, and Hudson Loughlin, a graduate student in MIT’s Department of Physics, suggest that the precision of these oscillators could be improved by manipulating the states that contribute to quantum noise.
- The team is working on an experimental test of their theory, which could lead to super-quantum precision in clocks, lasers, and other oscillators.
- This could be used to track extremely small differences in time, such as the fluctuations of a single qubit in a quantum computer or the presence of a dark matter particle.
- The researchers’ work, which is detailed in an open-access paper published in the journal Nature Communications, could advance our ability to keep time accurately and enable new technologies.
- The research is supported, in part, by the National Science Foundation.