Teleportation: the new frontier

Information of critical importance to governments, banks and even individuals could soon be far more secure, protected by the laws of physics rather than man-made code.

The movies have a lot to answer for.

Star Trek is the primary culprit, painting teleportation as the new passport to anywhere; but secret agents like 007 James Bond are also to blame, insinuating that the key to espionage success is to stay a gadget ahead of the enemy.

A breakthrough in the teleportation of secretsis a difficult concept for physicists to convey without being sidetracked into talk of fast cars, concealed weapons and metal-toothed adversaries.

ANU researchers in Canberra have announced that they are the first in the world to demonstrate the sharing of secrets via teleportation using quantum physics — but have ruled out beaming you to another planet for the time being.

The ANU team has focused on transmitting information, rather than objects, via teleportation. The astonishing feat of disembodying, transmitting, then reconstructing a message, from individually-meaningless signals received by several recipients, achieved recently in an ANU laboratory, places Australian scientists at the absolute frontier of teleportation technology.

This technology has the potential to improve the speed and security of computer systems around the world, with possible benefits including improved security for spy networks and financial computer networks. The breakthrough is also another important step towards the development of a quantum internet system which is faster, more reliable and more secure.

Head of the Quantum Optics Group in the Faculty of Science, Dr Ping Koy Lam, says the technology’s many applications show that the Group’s focus on teleportation of information could pay real dividends in improving communication technology.

The experiment involves the transmission of some encoded information — resembling a disembodied high-pitched whistle — via entangled laser beams, which are bounced off or through more than 150 lenses and mirrors spaced across a 2.4 metre-long stainless steel table. The ‘message’ is transmitted from a single sender on one side of the table to three recipients on the other. This process known as secret sharing.

The experiment was conducted by PhD student Andrew Lance (pictured, right) and Dr Thomas Symul (pictured, left) in collaboration with ANU staff Dr Warwick Bowen and Dr Lam and Professor Barry Sanders from the University of Calgary in Canada.

“The benefit of this technology is that the encrypted message can only be decoded by a majority of recipients. For example, if an encrypted message was sent to a spy network containing 15 individuals, a minimum of eight agents would be needed to access the message — limiting the chances of the message being infiltrated or deleted by a double-agent,” Mr Lance says.

“The system could also have major applications as a fail-safe mechanism in operating systems for a new generation of superfast quantum computers.”

Read more about  Andrew Lance

This research builds on teleportation work conducted by Dr Bowen and Dr Lam at ANU in 2002, when they teleported information between two points using a laser beam.

In their latest breakthrough, the Group used teleportation technology to disseminate information from one distributor to three recipients. The crucial difference in this experiment is that no one receiver can acquire the information in isolation, rather, a majority of the receivers need to collaborate to ‘decode’ the information.

“Teleportation of information has potential to improve the efficiency and security of future quantum computing and communication networks,” Dr Symul says.

“This demonstration will find applications in the corporate world as well as in the intelligence community by enabling unconditionally secure cryptography protocols.”

Secret sharing, which is used every day in computer networks, was first proposed by Professor Adi Shamir in 1979. The idea was to encode computer binary information, scramble it, and send it to multiple recipients. In order to retrieve the original information, a group of recipients bigger than a given threshold had to collaborate.

In 1999, Professor Richard E. Cleve extended Professor Shamir’s idea to the realm of quantum mechanics — a physics discipline that assumes energy exists in discrete units, a process known as quantum state sharing. Later on, in 2001, the ANU team’s collaborators, Professor Barry Sanders and Dr Tomàš Tyc of the newly launched Institute for Quantum Information Science at the University of Calgary, translated Professor Cleve’s quantum state sharing ideas into the optical domain, which then enabled the Quantum Optics Group to realise it experimentally for the first time ever.

In the ANU 2002 teleportation experiment, a sender, known for the purposes of the experiment as Alice, makes a partial measurement of a quantum stateand sends her results to a recipient, named Bob, who is then able to reconstruct it perfectly.

Quantum state sharing, achieved in the latest ANU experiment, enables Alice to send partial information of her secret quantum state to multiple Bobs who can then reconstruct it perfectly as soon as a majority of them are collaborating.

In the latest experiment, the information is lost to the third recipient. The fact that two recipients perfectly reconstruct the quantum state completely removes any information about it in the third player’s share, making the protocol absolutely secure against eavesdropping.

To comprehend this idea, think about this magic trick: a coin is hidden below one of three cups that are then manipulated. The game is then to retrieve the cup containing the coin, but it appears that whatever cup is chosen, the coin is never there. Usually the trick involves removing the coin at one point in time. Here we don’t need any ’magic’, but only to rely on the laws of quantum mechanics. Now when you choose a cup, it is possible to reconstruct the coin by combining what is underneath the two remaining cups. However, the coin will never be under a single cup.

Every experimental run took one day for the ANU team. The team would carryout preparations, such as aligning the optics and tuning the electronics and then would run the apparatus to acquire the results. Only at the end of the day, after the raw data had been analysed on a computer, did the team knowif their work had been a success or if a day’s work had been in vain. In total, three years were spent to build the laser entanglement apparatus, and one additional year was spent working on the quantum state sharing experiment. 

The successful results were published earlier this year in the prestigious journal Physical Review Letters.

Professor Sanders says: “Security is crucial for quantum networks that may someday deliver ultrafast solutions to certain computational problems and for communication that is impervious to eavesdroppers.

“Our experiment demonstrates that quantum networks can be protected from component failures and malice.”

http://photonics.anu.edu.au/qoptics/

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