New quantum microscope finds 'invisible' structures, scientists say

You've probably seen pictures of scientists looking at objects invisible to the naked eye under a microscope. In fact, microscopes are essential to our understanding of life.

They are equally integral to biotechnology and medicine, for example as we deal with diseases such as COVID-19. However, the best optical microscopes hit a fundamental hurdle—the bright lasers used to illuminate tiny objects can also destroy them.

In research published today in the journal Nature, our team of Australian and German researchers show that quantum technology offers a solution. We built a quantum microscope that probes biological samples more gently, which allows us to observe biological structures that would otherwise be impossible to see.

Creating a damage-avoidable microscope like ours is a long-awaited milestone on the international roadmap for quantum technologies. It represents the first step into an exciting new era of microscopy and broader sensing technologies.

Problems with laser microscopes

Microscopes have a long history. They are thought to have been first invented at the turn of the 17th century by Dutch lens maker Zacharias Janssen, who used them to counterfeit coins. The beginning of this twist led to the discovery of bacteria, cells, and basically all of microbiology as we now understand it.

The recent invention of lasers provides an intense new type of light that enables a whole new approach to microscopy. Laser microscopes allow us to observe living things in truly exquisite detail, 10,000 times thinner than a human hair. They won the 2014 Nobel Prize in Chemistry and have transformed our understanding of molecules such as DNA in cells and within cells.

However, laser microscopy faces a major problem. The quality that makes them successful - their strength - is also their Achilles heel. The best laser microscopes use light billions of times brighter than the sun on Earth. As you can imagine, this can cause severe burns!

In a laser microscope, biological samples can become sick or die within seconds. You can see this happening in real time in the fibroblast movie below, captured by our team member Michael Taylor.

Solution for quantum mechanics 'spooky action at a distance'

Our microscope avoids this problem. It uses a property called quantum entanglement, which Albert Einstein described as "spooky action at a distance".

Entanglement is an unusual correlation between particles, in our case the photons that make up a laser beam. We use it to train photons leaving the microscope to behave themselves, arriving at the detector in a very orderly fashion, which reduces noise.

Other microscopes require increased laser intensity to improve image clarity. By reducing noise, we can improve clarity without doing so. Alternatively, we can use a lower intensity laser to produce the same microscope performance.

A key challenge is generating quantum entanglement bright enough for laser microscopy. We do this by concentrating photons into laser pulses that are only a few billionths of a second long. This produces entanglement 100 million times brighter than previously used for imaging.

When used in a microscope, our entangled lasers provide up to 35% higher image clarity than other methods without damaging the sample. We use microscopy to image molecular vibrations within living cells, which allows us to see detailed structures that cannot be seen using traditional methods.

The improvement can be seen in the image below. These images, taken with our microscope, show molecular vibrations within a part of a yeast cell. The image on the left uses quantum entanglement, while the image on the right uses conventional lasers. I hope you agree, the quantum image is clearer and the areas where fat is stored inside cells (black blobs) and the cell walls (semi-circular structures) are more visible.

Towards the application of quantum sensing technology

Quantum technology is expected to have revolutionary applications in computing, communication and sensing. Australia's Commonwealth Scientific and Industrial Research Organisation (CSIRO) estimates they will create a global industry worth A$86 billion by 2040.

Quantum entanglement is the basis for many of these applications. A key challenge for quantum technology researchers is to demonstrate that it offers a definite advantage over current methods.

Financial institutions and government agencies already use entanglement to ensure secure communications. It's also at the heart of a quantum computer, which Google showed in 2019 can perform calculations that current conventional computers can't.

Quantum sensors are the final piece of the puzzle. They are expected to improve every aspect of how we see the world, from better navigation to better healthcare and medical diagnosis.

About a year ago, quantum entanglement was installed in a kilometer-scale gravitational-wave observatory. This allows scientists to detect massive objects farther away in space.

Warwick Bowen, Professor of Quantum and Precision Technologies at the University of Queensland, explained that our work shows that entanglement can provide absolute sensing advantages at more normal size scales and in a wide range of technologies. This could have big implications - not only for microscopy, but for many other applications such as global positioning, radar and navigation.