Scientists at the School of Physics, Trinity College Dublin, with collaborators at Yale University, USA, CentraleSupelec, France, and Nanyang Technological University in Singapore, have developed a tiny chip-scale laser system to harvest quantum fluctuations in semiconductor lasers on ultrasmall scales at unprecedented speed. The new technology can be used to underpin modern technologies’ requirements for randomly generated digital information.

Their technique, published today in Science, uses a specially designed hour-glass-shaped semiconductor laser to generate hundreds of tiny, random light waves that when detected with a device called a photodetector, can be transformed into random strings of ‘1’s and ‘0’s, or binary code, the foundation of modern digital communications.

The quest for this level of randomness is not automatically visible – but is vital for day-to-day digital communications. Randomness, particularly truly random randomness, is a valuable resource. Our ever-increasing reliance on e-commerce, internet based financial services and virtual social contacts, depends on how well and how fast these processes and interactions can be protected from unwanted access or observation through random-keys and random-number based encryption.

The problem is that today’s random numbers are usually at best, ‘pseudo-random’ numbers, generated by a computer using special algorithms to calculate a sequence of numbers that appears ‘random’. There is a key limitation in this approach: the ‘random sequence’ is only random to a point because it is generated from a deterministic algorithm meaning this encryption can be ‘cracked’ by a fast computer, or other avenue.

Given the potential scale of the problem researchers have started to explore physical sources of randomness, such as randomly generated steams of light, while acknowledging that the key technical challenges for physical random number generation are speed and scalability. Looking at how the physical properties of light-matter interactions might be harnessed, scientists looked at lasers, as Professor Ortwin Hess, from the School of Physics and the CRANN Institute at Trinity, explains:

“Normal semiconductor lasers emit coherent light, light that is uniform and that can be focused to a tight beam. To produce and amplify this light inside a laser, it first travels around a cavity through semiconductor gain materials. In previous designs of large-area semiconductor lasers this bouncing back and forth of light creates optical filaments – sections of the light that swiftly begin to act chaotically. The optical filaments are a bit like optical tornadoes. Once they form, they move about chaotically leading to chaotic and unruly light. However, these ‘optical tornadoes’ have a characteristic size and speed, so that in current semiconductor lasers there is an upper limit on how much randomness can be generated in space and at any given period of time.”

To create more random and spatially unconnected ‘optical tornados’ the team designed a new cavity-shape for the laser. The shape of a lasers’ cavity is important; it does for light what the body of different string instruments does for sound. Very different sounds can be created from different ‘shaped’ string instruments from a violin to double-bass, as the body of the instrument interacts with acoustic waves generated from vibrating strings.

In the case of (edge-emitting) semiconductor lasers, most cavities are cuboid in shape, but by changing this to an hour-glass shaped cavity, the team were able to induce optical tornados on much smaller scales ‘harvesting’ the quantum noise allowing a massively parallel arrangement and essentially more randomness at much higher speeds.

Professor Hess, who contributed much of the theory and interpretation of the semiconductor laser dynamics in the study said: “By creating an optical landscape that supports significantly smaller optical ‘mini-tornados’ that all very efficiently and directly ‘harvest’ the endless supply of quantum fluctuations via spontaneous emission on ultrafast time scales, making them both fast, scalable and truly random”

The team gained insight into the processes and cavity shapes likely to create this kind of laser from theories and experiments in laser cavities and semiconductor laser dynamics, quantum chaos and quantum nanophotonics.

Professor Hui Cao, from Yale University, said: “Our laser cavity serves as a resonator for optical waves, and we have designed its shape to resonate with many spatio-temporal modes of light so that light in these modes will be amplified. The emission from all these modes creates a broad frequency spectrum for intensity fluctuations, which we utilize for massively parallel ultrafast random bit generation.

Professor Hess added: “I have been working on spatio-temporal and quantum dynamics in semiconductor lasers since my PhD, so it is gratifying to return to it now with the knowledge gained from metamaterials and nanophotonics. Physically generating randomness based on a quantum process is a key to many applications in security and data modelling but, in particular, for quantum simulation of new materials that, in turn, help us to design and enable practical quantum technologies at room-temperature.”

‘Massively parallel ultrafast random bit generation with a chip-scale laser’, Kyungduk Kim, Stefan Bittner, Yongquan Zeng, Stefano Guazzotti, Ortwin Hess, Qi Jie Wang and Hui Cao is published in Science [DOI: 10.1126/science.abc2666]

Professor Jonathan Coleman, lead PI at AMBER, the SFI Centre for Advanced Materials and BioEngineering Research, and the School of Physics at Trinity College, has secured an European Research Council (ERC) Proof of Concept grant worth €150,000.

Fifty-five Proof of Concept grants were awarded to ERC grant holders across Europe this year as top-up funding to explore the commercial or societal potential of their work and to bring their work closer to the market. Prof Coleman is the only Irish recipient. This Proof of Concept project, named Print-SENSE, will examine the economic and technical feasibility of using nanomaterial based inks for high performance sensing applications, particularly within medical diagnostics.

On receiving the award, Prof. Coleman, AMBER PI and Trinity’s School of Physics commented: “I am delighted to be awarded this ERC Proof of Concept grant which gives me the opportunity to develop a market ready prototype based on the discoveries from my ERC funded FUTURE-PRINT grant. We have demonstrated that we can produce a low cost, reliable strain sensor using graphene nanocomposites, and shown that it is a significant improvement on traditional strain sensing technology, now we want to develop this further and ensure society has access to it.”

Stain sensors are incredibly valuable for a range of applications, but the team is focusing on medical diagnostics in particular. Strain sensors measure changes in mechanical strain such as the physical changes measuring pulse rate, or the changes in a stroke victim’s ability to swallow. A stain sensor detects this mechanical change and converts it into a proportional electrical signal thereby acting as mechanical-electrical converter. While there are stain sensors on the market currently, mostly made from metal foil, these have limitations in terms wearability, versatility, and most significantly, sensitivity.

Traditional metal foil gauges have a very limited working range of accurate measurement. This is due to the relative stiffness of metal foil gauges and this makes their integration into emerging technologies such as wearables, which require large working ranges, difficult. Replacing the metal with polymer-based nanocomposite sensor represents a step-change in terms of cost, ease of fabrication and sensitivity. The sensitivity of the stain sensor developed by Prof. Coleman and his team is 50 x more sensitive than the current industry standard strain sensors.

Prof. Coleman intends to build on his research to create a new generation of medical devices: “The work carried out previously by my group has focused on developing ink blends that contain a silicone based polymer and a nanomaterial such as graphene – that has excellent mechanical and electrical properties. We can deposit this ink using a variety of printing methods, from screen printing, to aerosol and mechanical deposition, and once the ink dries, it forms a super flexible polymer-nanomaterial composite film that extremely sensitive to external forces. An additional benefit of our very low-cost system is that we can control a variety of different parameters during the manufacturing process which gives us the ability to tune the sensitivity of our material for specific applications calling for detection of really minute strains. Currently, a research team led by Dr Dan O’Driscoll are exploring specific applications focusing on physical rehabilitation, real time breath and pulse monitors and early labour detection during pregnancy”

Professor Michael Morris, Director of AMBER, commented on the announcement, saying: “The awarding of this Proof of Concept grant to Professor Coleman acknowledges the significance of the research work he and his team are undertaking. This highly innovative area of research sits at the forefront of science globally with considerable potential for translation into economic and societal benefits to Ireland and beyond”.

Profs. Jonathan Coleman, Valeria Nicolosi and Stefano Sanvito, principal investigator at AMBER, CRANN, and Trinity’s School of Physics and School of Chemistry feature in the annual Clarivate Highly Cited Researchers list.

The list recognises 6,389 researchers globally who have demonstrated significant influence in their chosen field or fields through the publication of multiple highly cited papers during the last decade. Their names are drawn from the publications that rank in the top 1% by citations for field and publication year in the Web of Science™ citation index. The methodology underpinning the list draws on the data and analysis performed by bibliometric experts and data scientists at the Institute for Scientific Information™ at Clarivate.

This year, Clarivate have further categorised the 2020 list into two categories: researchers highly cited within a specific topic or subject area, and those that are cross-disciplinary in nature. Prof. Jonathan Coleman appears within the first cohort of 3,896 researchers with exceptional performance in a specific field. Further analysis reveals that Prof. Coleman is one of only 203 scientists featuring in the ‘materials science’ category. Prof. Stefano Sanvito and Prof. Valeria Nicolosi fall within the second cohort of 2,493 researcher categorised as ‘cross-disciplinary’ meaning their research publications and highly cited works can be found in journals across multiple topic areas.

Clarivate state that “The Highly Cited Researchers 2020 list helps identify that small fraction of the researcher population that contributes disproportionately to extending the frontiers of knowledge and gaining for society innovations that make the world healthier, richer, more sustainable and more secure”. They also recognise that in any such analysis there exists inevitable limitations in the analytical approach, and suggest a careful reading of the methodology is required.

Commenting on the achievement of Profs. Coleman, Nicolosi and Sanvito, Dr. Lorraine Byrne, Executive Director, AMBER said, “I wish to congratulate Prof. Coleman, Sanvito and Nicolosi on their achievement. Their internationally acclaimed research ensures that Ireland has a global reputation in materials science and cross-disciplinary research. It is because of our exceptional researchers that the AMBER centre can deliver on our mission of world leading materials science research for economic and societal impact, enhancing Irelands’ credentials as a hub for science and research”.

David Pendlebury, Senior Citation Analyst at the Institute for Scientific Information at Clarivate said: “In the race for knowledge, it is human capital that is fundamental and this list identifies and celebrates exceptional individual researchers who are having a great impact on the research community as measured by the rate at which their work is being cited by others.”

The full 2020 Highly Cited Researchers list and executive summary can be found online here

The core theme for Science Week 2020 is ‘Science Week - Choosing our Future’ focusing on how science can improve our lives in the future, and in the present. This will explore how science can help us to make positive choices that will impact the environment, our health, and our quality of life.

Our events will take place over zoom, and will use a combination of polls, chat questions and breakout rooms to ensure that your voice is heard, and your questions are answered.

AMBER will run three events for audiences of ALL ages and interests!

You can register by clicking the links below.

The Future of Health

Meet the AMBER team who are developing treatments so that you could regrow your own bone if it gets damaged, who are using 3D bioprinting to create organs, and are developing materials that could reverse sprinal cord injury.

The Future of Energy

What would you like the know about where science and scientsts will take the Future of Energy?Meet the AMBER team who are hydrogen fuel cells for transport and energy storage.

The Great Plastics Debate

Worldwide <5% of plastic is recycled. In Ireland we recycle < 1%. A solution is circularity – that materials are reused, repaired, restored, recycled whilst maintaining value. This workshop will introduce the scientists searching for solutions to problem plastic and their research that could reframe the plastics debate. This event forms part of The Re:Discovery Centre Lets Talk Science Festival