A group of physicists recently built the smallest engine ever created from just a single atom. Like any other engine it converts heat energy into movement — but it does so on a smaller scale than ever seen before. The atom is trapped in a cone of electromagnetic energy and lasers are used to heat it up and cool it down, which causes the atom to move back and forth in the cone like an engine piston.
The scientists from the University of Mainz in Germany who are behind the invention don’t have a particular use in mind for the engine. But it’s a good illustration of how we are increasingly able to replicate the everyday machines we rely on at a tiny scale. This is opening the way for some exciting possibilities in the future, particularly in the use of nanorobots in medicine, that could be sent into the body to release targeted drugs or even fight diseases such as cancer.
Nanotechnology deals with ultra-small objects equivalent to one billionth of a meter in size, which sounds an impossibly tiny scale at which to build machines. But size is relative to how close you are to an object. We can’t see things at the nanoscale with the naked eye, just as we can’t see the outer planets of the solar system. Yet if we zoom in — with a telescope for the planets or a powerful electron microscope for nano-objects — then we change the frame of reference and things look very different.
However, even after getting a closer look, we still can’t build machines at the nanoscale using conventional engineering tools. While regular machines, such as the internal combustion engines in most cars, operate according to the rules of physics laid out by Isaac Newton, things at the nanoscale follow the more complex laws of quantum mechanics. So we need different tools that take into account the quantum world in order to manipulate atoms and molecules in a way that uses them as building blocks for nanomachines. Here are four more tiny machines that could have a big impact.
1- Graphene engine for nanorobots
Researchers from Singapore have recently demonstrated a simple but nano-sized engine made from a highly elastic piece of graphene. Graphene is a two-dimensional sheet of carbon atoms that has exceptional mechanical strength. Inserting some chlorine and fluorine molecules into the graphene lattice and firing a laser at it causes the sheet to expand. Rapidly turning the laser on and off makes the graphene pump back and forth like the piston in an internal combustion engine.
The researchers think the graphene nano-engine could be used to power tiny robots, for example to attack cancer cells in the body. Or it could be used in a so-called “lab-on-a-chip” — a device that shrinks the functions of a chemistry lab into tiny package that can be used for rapid blood tests, among other things.
The rotors that produce movement in machines such as aircraft engines and fans all usually suffer from friction, which limits their performance. Nanotechnology can be used to create a motor from a single molecule, which can rotate without any friction. Normal rotors interact with the air according to Newton’s laws as they spin round and so experience friction. But, at the nanoscale, molecular rotors follow quantum law, meaning they don’t interact with the air in the same way and so friction doesn’t affect their performance.
Nature has actually already shown us that molecular motors are possible. Certain proteins can travel along a surface using a rotating mechanism that create movement from chemical energy. These motor proteins are what cause cells to contract and so are responsible for our muscle movements.
Researchers from Germany recently reported creating a molecular rotor by placing moving molecules inside a tiny hexagonal hole known as a nanopore in a thin piece of silver. The position and movement of the molecules meant they began to rotate around the hole like a rotor. Again, this form of nano-engine could be used to power a tiny robot around the body.
3- Controllable nano-rockets
A rocket is the fastest man-made vehicle that can freely travel across the universe. Several groupsof researchers have recently constructed a high-speed, remote-controlled nanoscale version of a rocket by combining nanoparticles with biological molecules.
In one case, the body of the rocket was made from a polystyrene bead covered in gold and chromium. This was attached to multiple “catalytic engine” molecules using strands of DNA. When placed in a solution of hydrogen peroxide, the engine molecules caused a chemical reaction that produced oxygen bubbles, forcing the rocket to move in the opposite direction. Shining a beam of ultra-violet light on one side of the rocket causes the DNA to break apart, detaching the engines and changing the rocket’s direction of travel. The researchers hope to develop the rocket so it can be used in any environment, for example to deliver drugs to a target area of the body.
4- Magnetic nano-vehicles for carrying drugs
Magnetic nanoparticles. Image credit: Tapas Sen, author provided
My own research group is among those working ona simpler way to carry drugs through the body that is already being explored with magnetic nanoparticles. Drugs are injected into a magnetic shell structure that can expand in the presence of heat or light. This means that, once inserted into the body, they can be guided to the target area using magnets and then activated to expand and release their drug.
The technology is also being studied for medical imaging. Creating the nanoparticles to gather in certain tissues and then scanning the body with a magnetic resonance imaging (MRI) could help highlight problems such as diabetes.
Scientists are exploiting the laws of quantum mechanics to create computers with an exponential increase in computing power.
Quantum computing
Since their creation in the 1950s and 1960s, digital computers have become a mainstay of modern life. Originally taking up entire rooms and taking many hours to perform simple calculations, they have become both highly portable and extremely powerful. Computers can now be found in many people’s pockets, on their desks, in their watches, their televisions and their cars. Our demand for processing power continues to increase as more people connect to the internet and the integration of computing into our lives increases.
Video source: In a nutshell - Kurzgesagt / YouTube. .View video details.
When Moore’s Law meets quantum mechanics
In 1965, Gordon Moore, co-founder of Intel, one of the world’s largest computer companies, first described what has now become known as Moore’s Law. An observation rather than a physical law, Moore noticed that the number of components that could fit on a computer chip doubled roughly every two years, and this observation has proven to hold true over the decades. Accordingly, the processing power and memory capacity of computers has doubled every two years as well.
Starting from computer chips that held a few thousand components in the 1960s, chips today hold several billion components. There is a physical limit to how small these components can get, and as they get near the size of an atom, the quirky rules that govern quantum mechanics come into play. These rules that govern the quantum world are so different from those of the macro world that our traditional understanding of binary logic in a computer doesn’t really work effectively any more. Quantum laws are based on probabilities, so a computer on this scale no longer works in a ‘deterministic’ manner, which means it gives us a definite answer. Rather, it starts to behave in a ‘probablistic’ way—the answer the computer would give us is based on probabilities, each result could fluctuate and we would have to try several times to get a reliable answer.
So if we want to keep increasing computer power, we are going to have to find a new way. Instead of being stymied or trying to avoid the peculiarities of quantum mechanics, we must find ways to exploit them.
In the computer that sits on your desk, your smartphone, or the biggest supercomputer in the world, information, be it text, pictures or sound is stored very simply as a number. The computer does its job by performing arithmetic calculations upon all these numbers. For example, every pixel in a photo is assigned numbers that represents its colour or brightness, numbers that can then be used in calculations to change or alter the image.
The computer saves these numbers in binary form instead of the decimal form that we use every day. In binary, there are only two numberss: 0 and 1. In a computer, these are known as ‘bits’, short for ‘binary digits’. Every piece of information in your computer is stored as a string of these 0s and 1s. As there are only two options, the 1 or the 0, it’s easy to store these using a number of different methods—for example, as magnetic dots on a hard drive, where the bit is either magnetised one way (1) or another (0), or where the bit has a tiny amount of electrical charge (1) or no charge (0). These combinations of 0s and 1s can represent almost anything, including letters, sounds and commands that tell the computer what to do.
Instead of binary bits, a quantum computer uses qubits. These are particles, such as an atom, ion or photon, where the information is stored by manipulating the particles’ quantum properties, such as spin or polarisation states.
In a normal computer the many steps of a calculation are carried out one after the other. Even if the computer might work on several calculations in parallel, each calculation has to be done one step at a time. A quantum computer works differently. The qubits are programmed with a complex set of conditions, which formulates the question, and these conditions then evolve following the rules of the quantum world—Schrödinger’s wave equation—to find the answer. Each programmed qubit evolves simultaneously; all the steps of the calculation are taken at the same time. Mathematicians have found that this approach can solve a number of computational tasks that are very hard or time consuming on a classical computer. Thespeed advantage is enormous—and grows with the complexity we can program (i.e. the number of qubits the quantum computer has).
Superposition
Individually, each qubit has its own quantum properties, such as spin. This has two values +1 and -1, but can also be in what’s called a superposition: partly +1 and partly -1. If you think of a globe, you can point to the North Pole (+1) or the South Pole (-1) or any other point in between: London, or Sydney. A quantum particle can be a in a state that is part North Pole and part South Pole.
A qubit with superposition is in a much more complex state than the simple 1 or 0 of a binary bit. More parameters are required to describe that state, and this translates to the amount of information a qubit can hold and process.
Entanglement
Even more interesting is the fact that we can link many particles, each in their state of superposition, together. We can create a link, called entanglement, where all of these particles are dependent upon each other, all their properties exist at the same time. All the particles together are in one big state that evolves, according to the rules of quantum mechanics, as a single system. This is what gives quantum computers their power of parallel processing—the qubits all evolve, individual yet linked, simultaneously.
Imagine the complexity of all these combinations, all the superpositions. The number of parameters needed to fully describe N qubits grows as 2 to the power N. Basically, this means that for each qubit you add to the computer, the information required to describe the assembly of qubits doubles. Just 50 qubits would require more than a billion numbers to describe their collective states or contents. This is where the supreme power of a quantum computer lies, since the evolution in time of these qubits corresponds to a bigger calculation, without costing more time.
For the particular tasks suited to quantum computers, a quantum computer with 30 qubits would be more powerful than the world’s most powerful supercomputer, and a 300 qubit quantum computer would be more powerful than every computer in the world connected together.
A delicate operation
An important feature of these quantum rules is that they are very sensitive to outside interference. The qubits must be kept completely isolated, so they are only being controlled by the laws of quantum mechanics, and not influenced by any environmental factors. Any disturbance to the qubits will cause them to leave their state of superposition—this is called decoherence. If the qubits decohere, the computation will break down. Creating a totally quiet, isolated environment is one of the great challenges of building a quantum computer.
Another challenge is transferring information from the quantum processor to some sort of quantum memory system that can preserve the information so that we can then read the answer. Researchers are working on developing ‘non-demolition’ readouts—ways to read the output of a computation without breaking the computation.
What are quantum computers useful for?
A lot of coverage of the applications of quantum computers talk about the huge gains in processing power over classical computers. Many statements have been made about being able to effortlessly solve hard problems instantaneously but it’s not clear if all the promises will hold up. Rather than being able to solve all of the world’s financial, medical and scientific questions at the press of a button, it’s much more likely that, as with many major scientific projects, the knowledge gain that comes from building the computers will prove just as valuable as their potential applications.
The nearest term and most likely applications for quantum computers will be within quantum mechanics itself. Quantum computers will provide a useful new way of simulating and testing the workings of quantum theory, with implications for chemistry, biochemistry, nanotechnology and drug design. Search engine optimisation for internet searches, management of other types of big data and optimising other systems, such as fleet routing and manufacturing processes could also be impacted by quantum computing.
Another area where large scale quantum computers are predicted to have a big impact is that of data security. In a world where so much of our personal information is online, keeping our data—bank details or our medical records—secure is crucial. To keep it safe, our data is protected by encryption algorithms that the recipient needs to ‘unlock’ with a key. Prime number factoring is one method used to create encryption algorithms. The key is based on knowing the prime number factors of a large number. This sounds pretty basic, but it’s actually very difficult to figure out what the prime number factors of a large number are.
Classical computers can very easily multiply two prime numbers to find their product. But their only option when performing the operation in reverse is a repetitive process of checking one number after another. Even performing billions of calculations per second, this can take an extremely long time when the numbers get especially large. Once numbers reach over 1000 digits, figuring out its prime number factors is generally considered to take too long for a classical computer to calculate—the data encryption is ‘uncrackable’ and our data is kept safe and sound.
However, the superposed qubits of quantum computers change everything. In 1994, mathematician Peter Shor came up with an algorithm that would enable quantum computers to factor large prime numbers significantly faster than by classical methods. As quantum computing advances we may need to change the way we secure our data so that quantum computers can’t access it.
Beyond these applications that we can foretell, there will undoubtedly be many new applications appearing as the technology develops. With classical computers, it was impossible to predict the advances of the internet, voice recognition and touch interfaces that are today so commonplace. Similarly, the most important breakthroughs to come from quantum computing are likely still unknown.
Two teams from the University of NSW (UNSW) are using silicon to create extremely coherent qubits in new ways, which opens the door to creating quantum computers using easy to manufacture components. One team is focussing on using silicon transistors like those in our laptops and smartphones.
The other UNSW-led team is working to create qubits from phosphorus atoms embedded in silicon. In 2012, this team created atom-sized components ten years ahead of schedule by making the world’s smallest transistor.
They placed a single phosphorus atom on a sheet of silicon with all the necessary atomic-sized components that would be needed to apply a voltage to the phosphorus atom, giving it its spin state in order to function as a qubit.
The nuclear spins of single phosphorus atoms have been shown to have
the highest fidelity (>99%) and
longest coherence time (>35 seconds)
of any qubit in the solid state making them extremely attractive for a scalable system.
A team at the University of Queensland is working to develop quantum computing techniques using single photons as qubits. In 2010, this team has also conducted the first quantum chemistry simulation. This sort of a task involves computing the complex quantum interactions between electrons and requires such complicated equations that performing the calculations with a classical computer necessarily requires a trade-off between accuracy and computational feasibility. Qubits, being in a quantum state themselves, are much more capable of representing these systems, and so offer great potential to the field of quantum chemistry.
This group has also performed a demonstration of a quantum device using photons capable of performing a task that is factorially difficult – i.e. one of the specific tasks that classical computers get stuck with.
Large sums of money are being invested into Australian quantum computing research. In 2014, the Commonwealth Bank made an investment of $5 million towards the .Centre of Excellence for Quantum Computation and Communication Technology at the University of New South Wales. Microsoft has invested more than $10M in engineered quantum systems at University of Sydney, also in 2014.
It’s not very likely that in 20 years we’ll all be walking around with quantum devices in our pockets. Most likely, the first quantum computers will be servers that people will access to undertake complex calculations. However, it is not easy to predict the future, who would have thought fifty years ago, that we would enjoy the power and functionality of today’s computers, like the smartphones that so many of us now depend upon? Who can tell what technology will be at our beck and call if the power of quantum mechanics can be harvested?
Since the days of Einstein, scientists have been trying to directly observe how light behaves both as a particle and a wave at the same time. Now, the first-ever snapshot of this dual nature has been captured, potentially opening up a new route towards quantum computing.
When UV light hits a metal surface, it causes an emission of electrons. Albert Einstein explained this ‘photoelectric’ effect by proposing that light – thought to only be a wave – is also a stream of particles.
But no experiment has ever been able to capture both of these ‘split personalities’ of light at the same time. The closest researchers of quantum mechanics have come is seeing either wave or particle, but always at different times.
Now, researchers at École Polytechnique Fédérale de Lausanne (EPFL) in Switzerland and Trinity College and the Lawrence Livermore National Laboratory in the US have done an experiment with a clever twist: using electrons to image light. The team is the first to capture a single snapshot of light behaving simultaneously as both a wave and a stream of particles particle. The breakthrough work, spearheaded by Fabrizio Carbone at EPFL, was published today in the journal Nature Communications.
A new take on a classic effect
The experiment is set up like this: A pulse of laser light is fired at a tiny metallic nanowire. The laser adds energy to the charged particles in the nanowire, causing them to vibrate. Light travels along this tiny wire in two possible directions, like cars on a highway. When waves travelling in opposite directions meet each other, they form a new wave that looks like it’s standing in place. Here, this standing wave becomes the source of light for the experiment, radiating around the nanowire.
The imaging was done at EPFL’s ultrafast energy-filtered transmission
electron microscope – one of only two in the world. (Photo: EPFL.)
This is where the experiment’s trick comes in: The scientists shot a stream of electrons close to the nanowire, using them to image the standing wave of light. As the electrons interacted with the confined light on the nanowire, they either sped up or slowed down. Using an ultrafast microscope to image the position where this change in speed occurred, Carbone’s team could now visualise the standing wave, which acts as a fingerprint of the wave-nature of light.
While this phenomenon shows the wave-like nature of light, it also simultaneously demonstrates its particle aspect. As the electrons pass close to the standing wave of light, they ‘hit’ the light’s particles – the photons – thereby either accelerating or slowing down their speed. This change in speed appears as an exchange of energy ‘packets’ (quanta) between electrons and photons. The very occurrence of these energy packets shows that the light on the nanowire behaves as a particle.
New route towards quantum computing?
“This experiment demonstrates that, for the first time ever, we can film quantum mechanics – and its paradoxical nature – directly,” says Carbone. In addition, the importance of this pioneering work can extend beyond fundamental science and to future technologies. As Carbone explains: “Being able to image and control quantum phenomena at the nanometre scale like this opens up a new route towards quantum computing.”
