How MIT Scientists Achieved the Impossible: Controlling Quantum Randomness

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10 Aug 2023

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Quantum physics is full of surprises and mysteries. One of them is the phenomenon of quantum randomness, which means that some events in the quantum world are completely unpredictable and impossible to control. For example, you can never know for sure when a radioactive atom will decay, or when a photon will pass through a slit in a double-slit experiment. These events are governed by chance, and no matter how much you try, you can’t influence their outcomes.

But what if you could? What if you could somehow manipulate quantum randomness and make it work in your favor? Imagine the possibilities for computing, sensing, and encryption. You could create more powerful and efficient algorithms, detect the faintest signals, and secure your data with unbreakable codes.

This may sound like science fiction, but it’s not. A team of researchers from the Massachusetts Institute of Technology (MIT) has achieved a milestone in quantum technologies, demonstrating for the first time the control of quantum randomness. They published their groundbreaking results in the journal Science on July 13, 2023.

What is quantum randomness and why is it important?

Quantum randomness is a fundamental feature of quantum physics, which describes the behavior of the smallest particles in nature, such as electrons, photons, and atoms. Unlike classical physics, which assumes that everything can be measured and predicted with certainty, quantum physics reveals that some things are inherently uncertain and probabilistic.

This means that there are limits to what we can know and do in the quantum realm. For instance, we can’t measure the exact position and momentum of an electron at the same time, according to Heisenberg’s uncertainty principle. We can only assign probabilities to different possible outcomes, and observe them when we perform an experiment.

Quantum randomness also implies that there are fluctuations or changes in the quantum state of a system, even when it is isolated from any external influence. For example, even in a vacuum, which is supposed to be empty of matter and light, there are fluctuations in the electromagnetic fields. These fluctuations are called vacuum fluctuations, and they are responsible for many fascinating phenomena that quantum scientists have discovered over the past hundred years.

Some examples of these phenomena are:

The Casimir effect: When two metal plates are placed very close together in a vacuum, they experience an attractive force due to the vacuum fluctuations.
The Lamb shift: When an electron jumps between two energy levels in a hydrogen atom, it emits or absorbs a photon with a slightly different frequency than expected due to the vacuum fluctuations.
The Hawking radiation: When a black hole evaporates, it emits radiation due to the vacuum fluctuations near its event horizon.

Quantum randomness is not only interesting from a theoretical perspective, but also from a practical one. It has many applications in various fields of science and technology, such as:

Quantum cryptography: Using quantum randomness, we can generate secure keys for encrypting and decrypting messages. These keys are impossible to crack or copy by an eavesdropper, thanks to the laws of quantum physics.
Quantum metrology: Using quantum randomness, we can enhance the precision and sensitivity of measurements. For example, we can use entangled photons to measure distances or angles with higher accuracy than classical methods.
Quantum computing: Using quantum randomness, we can perform computations that are impossible or inefficient with classical computers. For example, we can use superposition and entanglement to explore multiple solutions simultaneously or factor large numbers faster.

How did MIT scientists control quantum randomness?

The MIT team wanted to go beyond using quantum randomness for their applications. They wanted to control it and shape it according to their needs. To do this, they used an optical system called an optical parametric oscillator (OPO), which is a device that converts one photon into two photons with lower frequencies.

The OPO is a natural source of random numbers, because the process of photon splitting is random and unpredictable. By measuring the intensity or phase of the output photons from the OPO, we can generate strings of bits (0s and 1s) that are completely random.

However, sometimes we don’t want completely random numbers. Sometimes we want biased or skewed numbers that favor one outcome over another. For example, if we want to simulate a coin toss that has a 70% chance of landing on heads and a 30% chance of landing on tails, we need biased random numbers that reflect this probability distribution.

The MIT team found a way to create biased random numbers from the OPO by injecting a weak laser “bias” into it. The bias laser acts like a tuning knob that allows them to adjust the probability distribution of the output photons from the OPO. By changing the frequency or phase of the bias laser, they can make the output photons more likely or less likely to have certain values.

This is equivalent to controlling quantum randomness from the vacuum fluctuations that drive the OPO. The researchers showed that they can tune the bias laser to generate any probability distribution they want, from uniform (completely random) to delta (completely deterministic).

What are the implications and challenges of controlling quantum randomness?

The ability to control quantum randomness from the vacuum opens up new possibilities for probabilistic computing and weak field sensing. Probabilistic computing is a paradigm that leverages the intrinsic randomness of certain processes to perform computations. It doesn’t provide a single “right” answer, but rather a range of possible outcomes each with its associated probability.

This makes it well-suited to simulate physical phenomena and tackle optimization problems where multiple solutions exist and where exploration of various possibilities can lead to a better solution.

Weak field sensing is a technique that uses quantum randomness to detect very small signals, such as magnetic fields or gravitational waves. By controlling quantum randomness, we can enhance the signal-to-noise ratio and improve the sensitivity and resolution of the measurements.

However, controlling quantum randomness also poses some challenges and limitations. One of them is the trade-off between speed and quality. The more we bias the output photons from the OPO, the slower we generate random numbers. This means that we have to balance between the desired probability distribution and the rate of random number generation.

Another challenge is the verification and validation of the output photons from the OPO. How can we be sure that they are truly random and follow the intended probability distribution? How can we test and certify them for practical applications? These are open questions that require further research and development.

Conclusion

Controlling quantum randomness from the vacuum is a remarkable achievement that demonstrates the power and potential of quantum technologies. It also raises new questions and challenges that will inspire future innovations and discoveries.

As Charles Roques-Carmes, one of the lead authors of the study, said:

“We hope this work will stimulate further research in this direction, as there are still many open questions regarding how far we can push this control, what are its ultimate limits, and what new applications it may enable.”

What do you think about controlling quantum randomness? Do you find it exciting or scary? Share your thoughts with us in the comments below!

References

Controlling Quantum Randomness from the Vacuum | MIT Institute for Soldier Nanotechnologies
Scientists demonstrate control over quantum randomness using laser bias | Interesting Engineering
Controlling Quantum Randomness From the Vacuum | The Quantum Insider
Impossible Science: MIT Scientists Successfully Demonstrate First-Ever Control over Quantum Randomness | The Debrief
Controlling quantum randomness from the vacuum | EurekAlert!

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