Features

A team, including Oxford University scientists, has achieved a new record for storing and retrieving data from an optical quantum memory, our friends PhysOrg.com report.

The researchers achieved a data rate in excess of 1GHz, 100 times what is possible with existing quantum memories, they explain in Nature Photonics. Such a speedy memory would be a key component of any future quantum computing or communications device.

The result was achieved by firing pulses of thousands of photons encoded with data into a cesium vapor cell. The vapor turns the pulses into a spin wave, and the information can be retrieved by a read pulse that converts the spin wave back into an optical signal that is picked up by a detector.

Ian Walmsley, of Oxford University's Department of Physics, told PhysOrg's Lisa Zyga: 'There are a few steps that are required [to achieve high bandwidth], but the main approach is to use atoms with a higher energy storage state, and to apply more sophisticated control pulse methods.'

'Our plans are to demonstrate the operation of the memory at the quantum limit, using an external source of nonclassical light.'

The team note that the bandwidth was limited only by the response time of the detector, so in theory the quantum memory could be capable of even larger bandwidths. Their method, based on a Raman interaction, could be applied to other storage media (such as cold gases and solid state).

Ian adds: 'Challenges for the future in general are to increase the number of bits the memory can store and the readout efficiency of the memories to the point when they can be used in applications such as quantum communications links.'

In films and books black holes capture unwary spaceships and planets, gobble up whole galaxies or offer portals to other parts of the Universe.

So the idea that, with the start of the Large Hadron Collider (LHC), physicists finally had a machine powerful enough to, potentially, create ‘mini’ black holes caused some alarm.

But what do we really know about black holes? And how would a ‘mini’ one be different from their giant cousins lurking out there in space?

‘The simplest black holes are objects with a singularity in the centre and that are surrounded by an ‘event horizon’,’ explains Cigdem Issever of Oxford University’s Department of Physics. ‘Once something comes closer to the black hole than the radius of the event horizon, it is not able to leave: even light can’t escape and so the name ‘black hole’ was given to these objects by John Archibald Wheeler back in 1967.’

A hole in the Sun
Producing black holes turns out to be about mass (energy): squeeze mass into a sphere with a radius equal to what’s known as the ‘Schwarzschild radius’ – a threshold beyond which gravity causes an object of a certain density to collapse in on itself – and a black hole will form.

‘In fact the size of the Schwarzschild radius is directly proportional to the amount of mass that is squeezed in, as well as being directly proportional to the strength of gravity,’ Cigdem tells me.

‘For example, in order to form a black hole out of our Earth, you would need to squeeze its mass into a sphere about the size of a marble (radius 8.9 mm). By comparison the Schwarzschild radius of the sun is about 3 km.’

So what would happen if we swapped our Sun for a black hole?

‘If we replaced our Sun with a black hole of the same mass, surprisingly, not much would change in our solar system. The planets’ orbits would stay the same because the gravitational field that the black hole would produce would be exactly the same as that of the Sun. Although, admittedly, the solar system would be a bit dark and cold!’

But Cigdem’s interest in black holes isn’t theoretical, as a particle physicist she will be searching for signatures of ‘mini’ black holes in the LHC collisions:

‘I became interested in them as a particle physicist back in 2003 because extra dimension models predicted that they may be produced in high-energetic cosmic rays and, if so, even in particle accelerators. If we are really able to produce them, they could give us experimental insights into quantum gravitational effects.’

She hopes that studying them may lead to a formulation of a theory of quantum gravity: marrying Einstein’s theory of general relativity (which describes gravity on large scales) with quantum mechanics (which describes physics at very small distances).

The LHC is colliding protons on protons. These protons are made up of smaller constituents, the so called ‘partons’ which are actually the particles the LHC is colliding. The Schwarzschild radius of two colliding partons – quarks and gluons for example – at the LHC is at least fifteen orders of magnitudes below the Planck length - the smallest distance or size an object can achieve in our conventional universe.

‘This means that, in conventional models of physics, there is no way a black hole could be produced in a collision of two partons. However, there are models on the market suggesting that the strength of gravity could become significantly larger at very small distances, up to 10 to the 38th [10 with 38 zeroes] times stronger,’ she comments.

‘If this is true then the Schwarzschild radius of two colliding partons becomes large enough that, at the LHC centre-of-mass energy, two partons passing each other at their Schwarzschild radius is not so unlikely anymore. So, we may be able to produce microscopic black holes after all.’

Who's afraid of a 'mini' black hole?
So what would these tiny black holes be like? Should we be worried about them?

Cigdem tells me: ‘According to Stephen Hawking, they will not be that black in fact. They will evaporate with time approximately following a black body radiation spectrum. The evaporation rate will be inversely proportional to the black hole mass.’

‘Astronomical black holes are so massive that their evaporation rate is negligible. In contrast, mini black holes are hot: unimaginably hot. The core of our Sun is at around 15,000,000 degrees Kelvin - to get close to the temperature of a mini black hole you would need to add another 42 zeroes.’

‘What this incredible temperature means is that mini black holes of tiny mass ‘evaporate’ into the far, far colder space around them almost infinitely fast. Their expected lifetime is around one octillionth of a nanosecond – so that they pop out of existence again almost as soon as they are created.’

If they do appear they will almost instantaneously burst into many particles which the ATLAS detector should pick up.

‘These particles will have very striking features. The total energy deposited in the detector will be of the order of a few TeVs [Tera electron volts] and the number of final state particles will be large. Black hole signatures can hardly be imitated by any other new physics so, if they are being produced, it will be hard to miss them,’ Cigdem adds.

So the hunt begins: on 30 March the LHC is aiming for collision energies of 7 TeV that may enable us to see some quantum gravity effects for the first time.

At the beginning of this year Dr Cigdem Issever moved to CERN to coordinate the efforts of the ATLAS Exotics physics group.

Read more about this topic in What black holes can teach us by Sabine Hossenfelder and the LHC Safety Assessment Group report.

In the second of a series of articles marking the 10th anniversary of the Human Genome Project [HPG], OxSciBlog talks to Professor Chris Ponting of the MRC Functional Genomics Unit at Oxford University.

Chris explains what we can learn about ourselves by comparing our DNA with the genomes of other animal species.

OxSciBlog: What genome efforts have you been involved with?
Chris Ponting: It all started when I was phoned up and asked whether I’d like to help coordinate a set of analyses for the Human Genome Project. Of course, I jumped at the chance but still feel it ironic that, as someone who gave up biology at school at 16 to focus on a training in physics, I was offered this chance. Since then I’ve worked with many people and groups from around the world on the genomes of the mouse, rat, dog, marsupial, duck-billed platypus, chicken, zebra finch, fruit fly and lizard.

OSB: What can all this genetic information from different species tell us?
CP: Having DNA from different species is crucial to understanding the human genome. Each additional genome is an evolutionary yardstick against which human DNA can be compared.

For example, when you ‘walk’ down each chromosome you see DNA letters that are the same in us and in mice – they have stayed unaltered over tens of millions of years because of their biological importance. This is because spontaneous changes (mutations) in important, conserved DNA tend not to be carried over into subsequent generations as they cause illness or even death.

By separating DNA that has remained relatively unaltered across animal evolution from DNA that has changed rapidly, we efficiently separate ‘functional’ DNA from ‘junk’ DNA. One of the biggest surprises has been the amount of ‘junk’ DNA. Only about 10% of the human genome appears to ‘do’ something, the rest appears not to be important at all.

OSB: What does your own research focus on?
CP: Genomics is rapidly permeating into many areas of biology and medicine, and we have tried our hand at many things over the past few years. My group is trying to understand which genetic changes cause disorders such as autism, intellectual disability or Parkinson’s disease, whilst thinking about how zebra finches learn how to sing or how the platypus senses its prey under water.

It has been particularly enjoyable discovering that there are no more genes making protein in the human genome than they are in a microscopic nematode worm. Science is good like that: its perspective is often humbling.

We can learn a lot just from the gene sequences, seeing how they’ve been conserved or have changed across the millennia and across the tree of life. But most of what we do is to solve puzzles: putting together pieces of information drawn from diverse areas such as evolution, genetics, natural history and clinical medicine. Synthesising this information is often very rewarding and tells us something new.

OSB: What can we look forward to in the future?
CP: As sequencing becomes cheaper, some are advocating sequencing the DNA from all animals. Certainly, most of the species that are important to biology and medicine are being, or have been, sequenced. I look forward to seeing soon the DNA sequence of many animals, from ants to zebras.

Nowadays, we’re looking past the DNA that encodes protein to the hundreds of millions of DNA letters that appear to be doing something, but certainly don’t make protein. It is this ‘genomic dark matter’ that we need to illuminate if we are to better understand the differences between ourselves, or even between us and other animals.

OSB: Might this research hold benefits for human health?
CP: Sequencing DNA is becoming cheaper and cheaper. The first human genome, sequenced ten years ago, cost a staggering $3 billion. Soon one genome will cost $1000. With these plummeting costs come the realisation that individuals’ genomes can be sequenced to try and understand the DNA changes that cause rare or common diseases.

Some might be fearful of what their own genomes could tell them: might they, and perhaps their children, carry some genetic change that predisposes them to disease? In the vast majority of cases, the outcomes aren’t likely to be as simple or as clear cut as that.

I think there are two things to be said here. First, everyone’s genomes carry many changes (‘genetic blemishes’) that give marginal changes to disease susceptibility. In this sense, everyone’s genomes are far from ‘perfect’. Second, despite being able to read someone’s genomes, we are a long way from understanding them so, as scientists and clinicians, we are usually far from assigning single DNA changes to diseases.

OSB: You suggest that these approaches could lead to fewer animals being used in research. How?
CP: All our work is done in the computer and, as time has gone on, we’ve become more sophisticated at spotting genes that do equivalent things in different species. As a result, we have separated genes which are less informative from others which, if studied in model organisms such as fruit flies and mice, immediately provide insights into human biology. Also, evolutionary approaches can now make good guesses of what a gene’s functions are, all of which reduces the number of uninformative experiments. Computational studies are certainly doing their bit to reduce the use of animals in science.

What do shells, solar panels and DVDs have in common?

At the atomic scale they are ‘amorphous’, that is – unlike crystals – they are built from irregular arrangements of atoms.

As Andrew Goodwin of Oxford University’s Department of Chemistry explains this irregularity is important: it’s what allows shells to grow their curved edges and gives silicon its incredibly useful electronic properties.

But for scientists this irregularity also makes such materials tricky.

‘Our main technique for establishing what materials look like on the atomic scale is crystallography,’ Andrew tells me, ‘and this relies explicitly on the existence of a repeating arrangement of atoms in order to work. So the problem of studying amorphous materials with their seemingly-random arrangements of atoms has remained just that: a problem.’

Now, Andrew, and colleagues from Cambridge and Ohio, report in this week’s Physical Review Letters how tantalising crystallographic clues could offer a new approach to understanding amorphous materials.

‘For decades we’ve known that the ring-like patterns amorphous materials produce in crystallographic experiments contain limited information about the surrounding environment of each atom,’ Andrew comments, ‘but the big question has always been how to use this to create a coherent picture of the structure of a material.’

He explains that the new approach comes from the ‘neighbourly behaviour’ of atoms which means that similar atoms should experience a similar environment.

‘The spacing of the rings in the 'ring-like pattern' is related to the distances between atoms in the material, and the intensity of the rings is essentially related to how many neighbours each atom has,’ Andrew tells me.

‘So, using silicon as an example, a typical analysis of its corresponding crystallographic pattern would have told us that the distance between silicon atoms is about 235 trillionths of a metre [picometres], and that on average each silicon atom has four neighbours.’

Yet this information alone isn’t enough to build reliable models of what the atomic structure of a material such as silicon actually looks like.

Such models fail because they rely on the average ‘neighbourly behaviour’ of the atoms which means in these models some silicon atoms can have three neighbours if others have five – something other techniques such as spectroscopy show is incorrect.

The new insight relates to the fact that such experiments are sensitive to the number of neighbours each atom has, so an atom with three neighbours would appear as a different ‘type’ of atom to one with five neighbours.

‘Because there is only one ‘type’ of atom observed for silicon we know that not only is the average number of neighbours equal to four, but that each silicon atom must have exactly four neighbours,’ Andrew adds.

‘If we incorporate this extra information when building a model, the answer seems to fall out almost straight away. We simply tell our program how many different types of atom there are, and in what proportions, and this is enough to produce a realistic model from the ring-like patterns.’

The findings suggest that crystallography might, after all, be able to unlock the structural secrets of some of Nature’s most irregular materials: opening the way for new kinds of science and powerful new technologies.

Dr Andrew Goodwin is based at Oxford University's Department of Chemistry.

Image: Ring-like pattern observed using crystallographic techniques, in this example silicon has been used.

The first UK trial of a promising new retinal implant technique is to be led by Oxford University researchers.

The technology, developed by the firm Retinal Implant, AG, involves implanting a device underneath a patient's retina.

The device itself is light sensitive, with a 1,500 pixel array, and is stimulated by the natural image focused by the eye - eliminating the need for an external camera (typically mounted on spectacles).

Retinal implants hold particular promise for the treatment of retinitis pigmentosa (RP) a form of inherited retinal degeneration affecting approximately 200,000 people worldwide that typically causes severe vision problems in adulthood.

The trial will be led by Professor Robert MacLaren of Oxford University's Nuffield Laboratory of Ophthalmology. 'I have been working in developing new treatments for patients with retinal diseases for many years and I was initially sceptical about the role of electronic devices,' he said.

'However, this recent work by the Retina Implant team is very impressive indeed and I would now certainly consider this technology as a viable treatment option for patients blind from RP.'

He described it as 'much more logical' to implant a device underneath the retina, as this is 'where the residual neurons are orientated towards the implant electrodes, because this should equate to a much higher pixel resolution.'

Making the implant itself light sensitive is, he believes, a major advance 'because the whole device can be contained within the eye. A power supply is fed through a battery behind the ear similar to a hearing aid.'

'This represents a true fusion of an electronic interface with the human central nervous system and we are likely now to learn a lot more about this technology as the trial progresses.' 

The Oxford-led clinical trial using the technology, which will take place at the John Radcliffe Hospital, is due to start later this year.

Images: courtesy of Retinal Implant, AG.