What has Quantum ever done for me?
Monday, Apr 16, 2018, 11:58 PM | Source: Pursuit
By Lloyd Hollenberg, David Simpson
A hangar sits in the middle of a decommissioned airfield in the English countryside.
Visits here are strictly by appointment only. The building teems with centuries' worth of scientific and engineering miscellanea: the first hovercraft, a Fleet Street printing press the size of two small buildings, and a retired nuclear missile.
Tucked in one corner is an inconspicuous device, an angular collection of pipes, wires and sockets. Yet, within this modest frame, in this hushed corner of the universe, a quantum adventure began.
Invented in 1955, the device is the Caesium Mk.1, the world's first ever atomic clock. It is now housed in the UK's Science Museum's large object store in Wroughton, Wiltshire.
The machine could equally be called a quantum clock because its fundamental tick-tock is determined by the movement of the smallest parts of a cesium atom – an element with particularly useful properties for measuring.
Finding an immutable, absolute second was one of the first practical applications of quantum mechanics. Other recent innovations, including GPS, can all be traced back to this original breakthrough.
And more are coming.
The famously "spooky" properties of atoms at a quantum level have inspired speculative applications that are still within the realm of science fiction. For example, super precise weather forecasting, Minority Report style hyper-personalised advertising, and the discovery of habitable planets have been mooted recently.
Most of these relate to quantum computing, an area that promises much but still exists primarily in theory. To become a reality, it needs large numbers of qubits – these are atoms whose photons and electrons have been programmed to be held in a particular state.
Quantum sensing, however, only needs one. That's why it is already here. Developments in drug design, medical diagnoses, and manufacturing are within reach.
The science is deceptively simple. Qubits are incredibly susceptible to the environment. Temperature, magnetic fields, vibrations, cosmic rays, and light can all make it collapse. Its fragility is why quantum computing – which requires millions of stable qubits – still isn't a reality.
However, it makes qubits perfect for sensing the smallest fluctuations in the world around it. Data gathered from their collapse can add a hitherto unattainable fine grain detail.
"We set up what you could call a quantum bubble, let it burst, repeat, and then learn about the environment," says Professor Lloyd Hollenberg, Deputy Director of the Centre for Quantum Computation and Communication Technology and the Thomas Baker Chair at the University of Melbourne.
Within the last decade these 'bubbles', or qubits, come with added bling. Experts have discovered the best way to house them is in a diamond.
"It's a robust cage that is chemically inert and bio-compatible making it an ideal sensor for biology," says Dr David Simpson, research fellow in quantum sensing at the University of Melbourne.
Less than one micrometre in size (which is 0.001 of a millimetre), these nanodiamonds are engineered to have a nitrogen vacancy (NV) which is a single nitrogen atom and a gap within the rigid lattice of carbon atoms. Using a combination of light and microwaves, the solitary nitrogen-vacancy complex is then programmed into a qubit.
"It makes for a tiny thermometer or magnetometer that can be applied inside biological systems, which is a harsh environment to operate. The output from these sensors can be reliably read out over long periods of time," says Dr Simpson.
He is now able to use thousands of these nanodiamonds to gain understanding of changes and properties at a cellular level and spatially locate them.
For example, if scientists previously wanted to know whether a biological system contained a magnetic field, which is integral for things like navigation in some animals, they would have to blend the entire system together and measure the average magnetic signal.
With quantum sensing they can keep the system intact, determine precisely which parts are magnetised, and to what degree.
Quantum is moving measurement from the crude to the precise.
"We have this cool toy," he says. "I've have been sitting down with biologists and neurologists and asking them if they have a problem we can help with."
Of course there is.
Dr Simpson is working with neurologists at the University of Melbourne to investigate how increased neuronal activity that occurs in disorders like epilepsy affects neurons in the brain.
"Our brains are constantly firing, generating heat," he says. "With epilepsy, neuronal networks go into overdrive. The question is, does this increased activity create more heat than in a healthy system? If it does, that may damage the neurons even more. So, can we take a neuron's temperature?"
Step forward quantum sensing. Using thousands of programmed nanodiamonds inside neuronal networks, Dr Simpson and colleagues are able to measure the temperature of the system at a nanoscale.
"We are exploring whether increased activity leads to a neural network running hot, and if it responds to certain drugs which act to reduce neuronal activity," says Dr Simpson. "That will tell us new and valuable information about the fundamentals of neuronal activity."
As well as being injected into a biological system, these quantum sensors can be engineered just below the surface on a thin membrane of ultra-pure diamond to create a quantum sensing chip.
It is already being applied in pharmacology, to understand the impact of drugs on cellular systems, in particular in respiratory diseases such as asthma.
Asthma restricts the airways by increasing cell stiffness. The current way for experts to measure a cell's rigidity in response to a drug is to place them on a bed of florescent beads. If the cell is relaxed, the beads move freely. If it is stiff, the movement is restricted.
However, the light, vital to track the movement of the beads, has adverse effects on the drug and the biological system under investigation, which muddies the picture.
"So, one application we are exploring is to take the florescent beads away and replace them with magnetic beads," says Dr Simpson. "We place the quantum sensor chip underneath and track the magnetic field, with no light exposed to the biological system."
The same quantum sensors are also being used to manipulate the quantum properties of other atoms, with staggering results.
When a patient undergoes an MRI scan, they are injected with a contrast agent, a substance that will help the machine take a snapshot of the body's inner workings.
These agents are deeply inefficient. A conventional machine only picks up 0.00001 per cent of the signals they emit. It gives a useful, but incomplete picture.
However, scientists are able to boost the signal of a contrast agent using a technique called hyperpolarisation.
Using a programmed nanodiamond quantum sensor, it is possible to align its nuclear spins in the same direction, thereby sending a clearer, more coherent signal.
"We discovered that we could use a NV centre as an entropy pump," says Professor Hollenberg, meaning it can be used to bring order to a chaotic state.
"If you think of randomly orientated nuclear spins in the molecule, this is a highly disordered state which gives rise to a very small magnetic signal. Using the NV we can align these nuclear spins one by one along an axis of our choice, thereby significantly enhancing the observed magnetic signal."
Scaled up, this quantum nudge means it is possible for the MRI machine to detect up to 50 per cent of the agent, according to new research.
In terms of resolution, it is like moving from cave paintings to the Renaissance in a matter of minutes.
To get the same result using conventional approaches would require magnetic fields up to 100,000 Teslas, which is approximately 10,000 times stronger than both our current state-of-the-art instruments and beyond our physiological limits. To put it another way, this is the same level of magnetic field found around a neutron star.
And this is just the start.
As Dr Simpson explains, these new quantum sensing tools reveal an unseen level of detail and reveal just how little we know.
"It is providing information that we haven't had access to before," he says. "The challenge is where to apply it. People don't know the answers to the questions we are asking.
"It's exciting. We're all explorers now."
Banner image: Paul Burston/University of Melbourne