Physicists set new record for quantum teleportation with matter qubits

Apr 16, 2013 by Lisa Zyga feature
Experimental setup for teleportation between single-atom quantum memories. Single atoms (gray spheres A and B) are trapped in optical cavities (blue cones) separated by a distance of 21 m. (a) Entanglement is generated between atom B and an ancilla photon C. (b) The atomic qubit at node A is mapped onto a photonic qubit A’ and a Bell-state measurement between the two photons is performed. (c) Detection of an event heralds the successful teleportation of the atomic qubit from node A to node B. Credit: Christian Nölleke, et al. ©2013 American Physical Society

(Phys.org) —In most demonstrations of quantum teleportation between remote atomic qubits, the atoms exist in free space. In a new study, scientists have discovered that trapping the atoms in optical cavities can overcome some of the previous obstacles facing matter teleportation, which enables an improvement in efficiency of almost 5 orders of magnitude and teleportation across a record-breaking distance of 21 m. These improvements in quantum teleportation could open the doors to realizing quantum networks with many nodes for teleporting qubits to various destinations.

The researchers, Christian Nölleke, et al., at the Max Planck Institute for at Garching, Germany, have published their study on the new scheme in a recent issue of Physical Review Letters.

"The greatest significance of our work is the dramatic increase in efficiency compared to previous realizations of matter-matter teleportation," Nölleke said. "Besides, it is the first demonstration of matter-matter teleportation between truly independent systems and constitutes the current record in distance of 21 m. The previous record was 1 m."

In , can be transmitted from one node to another in a quantum network without physically traversing the space in between. The technique could be used to transmit information in a secure way over very large distances, and can ultimately lead to worldwide .

Teleportation can be realized with either photonic qubits or matter qubits. In 2012, physicists teleported photonic qubits a record distance of 143 km. Teleporting matter qubits over long distances is more difficult than teleporting photonic because it requires quantum memories and a between light and matter. In a previous experiment, scientists have performed material teleportation without a strong light-matter interaction, and achieved a distance of 1 m. However, the low photon-collection efficiency in free space prevents scaling of that approach to larger distances.

In the new study, the physicists have eliminated this obstacle by trapping two remote single atoms in their own optical cavity. The optical cavity increases the photon collection efficiency and the interaction strength between atom and photon. Both effects lead to an increase in the number of "usable" photons. In the absence of a cavity, atom-photon entanglement can also be generated with high efficiency; however, the emission direction of the photons is random, so most of the photons will be lost.

During the teleportation process, the spin state of the atomic qubit at one node is mapped onto the polarization of a photonic qubit. At the second node, entanglement is simultaneously generated between a second atom and a second photon. Then the researchers performed a Bell-state measurement between the two photons, which destroys the two photons and projects the second atom onto the state of the first atom. This projection teleports the qubit between the atoms.

One of the important achievements of this scheme is that is has a success probability of 0.1%. Although this may not seem like a very high efficiency, it's nearly 100,000 times higher than that achieved in previous experiments. The main reason for the improvement is that, in contrast to previous demonstrations, the efficiency is not predominantly limited by single-photon collection efficiency. Instead, the limiting factor is the requirement to transmit and detect two photons simultaneously, which is inherent in the Bell-state measurement.

The performance of the special type of Bell-state measurement (purely photonic) is already close to the edge of what is possible with current technology (mainly limited by fiber losses and efficiencies of the detectors). To increase the efficiency of this stage, the scientists would have to use a different type of Bell-state measurement based on deterministic quantum gates. Fortunately, the current cavity system has the potential to straightforwardly implement such a Bell-state measurement.

"Future plans include to increase the light-matter interaction by using cavities that provide us with a higher atom-photon coupling strength," Nölleke said. "This would increase the efficiency of our protocol even further. Another prospect is to implement a different type of Bell-state measurement to increase the efficiency."

Since the atoms trapped in act as non-identical quantum memories, the scheme could have applications for building where identical network nodes are hard to realize. For larger network consisting of more than two nodes, the time is takes to teleport a quantum state must be shorter than the coherence time. In the current experiment, this time is 0.1 s and therefore smaller than coherence times in atoms (~1 s).

"Applications are the realization of quantum networks and the secure transmission of information using quantum key distribution at a global scale," Nölleke said. "Both applications require the transfer of quantum states over long distances. As we explain in the first paragraph of our paper, there is no classical technique to achieve this. There is, however, a clear strategy based on so-called 'quantum repeaters' (the quantum version of a classical repeater) and the utilization of teleportation to transfer quantum states over very ."

Explore further: Early computer oscillator could become a core part of quantum computers

More information: Christian Nölleke, et al. "Efficient Teleportation Between Remote Single-Atom Quantum Memories." PRL 110, 140403 (2013). DOI: 10.1103/PhysRevLett.110.140403
Also at: arXiv:1212.3127 [quant-ph]

Journal reference: Physical Review Letters search and more info website

4.4 /5 (36 votes)

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Higgsbengaliboson
2.6 / 5 (5) Apr 16, 2013
This kind of research for more feasible form of quantum internet came out couple of month ago and here quantum information can be passed using q-bit in optical computing method-passage of data transformation using teleportation.
holoman
2 / 5 (4) Apr 16, 2013
For further insight an invention patented and published 1n 1999.

http://www.coloss...age.net/
rkilburn81
1 / 5 (4) Apr 16, 2013
I know that the teleportation of complex matter (like people in Star Trek) is probably far too complicated to be feasible...
But could teleportation of simple matter, like hydrogen be feasible?
I imagine mining satellite orbiting a gas giant and quantum teleporting the hydrogen gas up to containers to be sent back to Earth as fuel.
Whydening Gyre
3.4 / 5 (9) Apr 16, 2013
To be clear, this is not matter transport. It is "state" transfer of info from one atom to another. Did the state od an atom of, let's say -helium, get transferred onto an atom of, let's say - hydrogen and did the hydrogen then become a helium atom?
NO. Therefore, matter teleportation did not occur.
Readers need to stop getting sucked in by the sci-fi verbiage and dwell on the facts.
DarkHorse66
3.3 / 5 (7) Apr 16, 2013
Here is the difference:
" Quantum teleportation is unrelated to the common term teleportation – it does not transport the system itself, and does not concern rearranging particles to copy the form of an object."
From: http://en.wikiped...ortation
Cheers, DH66
ValeriaT
1.5 / 5 (8) Apr 16, 2013
To be clear, this is not matter transport. It is "state" transfer of info from one atom to another.
The information as such doesn't exist without energy transfer. In classical physics no information can be transfered without energy transfer (the minimal amount of energy corresponds the mass of graviton and/or energy of CMBR photon by Landauer theorem). In AWT no energy can be transfered without mass transfer, no matter how minute such a matter is (its mass is related to energy with E=mc^2 equation). What was transfered here is the photon energy, but in form of longitudinal (scalar) waves of vacuum, i.e. in superluminal speed. Which is OK, because the mass of photon corresponds exactly the energy of its adjacent scalar wave (2-spin component) and vice-versa.
ValeriaT
1.5 / 5 (8) Apr 16, 2013
At the water surface analogy of dense aether model the solitons of surface ripples correspond the photons and the gravitational waves correspond the underwater sound waves. Now the question is, whether the surface ripples can ever spread without underwater sound waves? IMO every surface ripple makes an audible splash in the underwater, so that every surface solitons has its corresponding density fluctuation of underwater attached. After then we can imagine, that the state of two objects floating at the water surface at distance can be exchanged via underwater sound waves instead of surface ripples. At the moment when the mass of water transfered in this way would correspond the energy of surface ripple, both mechanism are fully equivalent. The underwater energy spreading is limited by its intensity, it's indeterministic with compare to surface energy spreading (it cannot be traced at the water surface reliably) - but it's much faster, than the surface wave spreading.
ValeriaT
1.5 / 5 (8) Apr 16, 2013
We can imagine the vacuum more realistically like the foam, where most of energy spreads along membranes of this foam like the transverse light wave. But some minute portion of energy can spread through bulk of foam bubbles - i.e. much higher speed, than the speed of light. Such an energy will vibrate the membranes of foam from all directions at the same moment, so we cannot trace its source reliably. Of course, under the situation, when we change the quantum state of one trapped atom inside of atom cavity, the state of another atom will change accordingly, so that the causality is still maintained here - but we cannot prove it experimentally: the transfer of information is too fast in this case.
ValeriaT
1.6 / 5 (7) Apr 16, 2013
it is the first demonstration of matter-matter teleportation
The previous experiments demonstrated only transfer of quantum state between photons trapped inside of boson condensate, not between massive atoms. Note that until the photon is not considered massive we cannot consider it a matter teleportation.
MRBlizzard
2 / 5 (4) Apr 17, 2013
There is a long lived meta-stable state of 57Fe. I was wondering if one could transfer the meta-stable nuclear state from one Fe to the other Fe.
antialias_physorg
3.7 / 5 (6) Apr 17, 2013
I think the article is a worded a bit confusingly.
When people think about 'teleportation' they often think that something happens faster than the speed of light - which is not so in this experiment, as the state information of one atom is transferred via a photon to the other atom.

Also what is important to understand is that while such entanglement can be used for secure encrytion/decryption processes the encryption/decryption process itself does NOT constitute a transfer of information (encryption does not add information to a signal). This is why such a process can be 'spooky action at a distance' (or 'faster than light') without breaking any laws.

The transfer of the information itself is still limited by the speed of light.
Whydening Gyre
2.3 / 5 (3) Apr 19, 2013
The transfer of the information itself is still limited by the speed of light.

Exactly.
However, I'm still a little confused as to how this is so useful in encryption... I mean - don't you still have to then tell the decrypting station what the code is so it can decode the signal?
antialias_physorg
3.7 / 5 (3) Apr 19, 2013
The usefulness as an encryption device works like this:

You add the state of one entangled entity (modulo) at the sender and subtract the conjugate of its entangled pair (modulo) at the receiver.
You first need to distribute this key (via a standard channel is OK)
The state of the entangled entities are still undetermined as of the time of use - but as they are entangled, when you measure/use one (for encryption) you determine the other (the one used for decryption)

What is so hot about this is that it allows the receiver to know when someone is attempting to read the key (man-in-the-middle-attack), as reading a quantum system disturbs it. Read: the man-in-the-middle breaks the entaglement and the encryption/decryption scheme starts to fail. Which is very noticeable at the reciving end.
At that point the receiver can notify the sender that the channel is compromised and they can stop communicating/switch protocol immediately.
metainfo
not rated yet Apr 20, 2013
Definition of a p-XOR (read: 'pixor', meaning: 'photonic XOR') Gate:
An optical illusion, a magician's trick, what you see is what you believe.

One can only see atom's quantum states through photon interactions with detectors. Terefore, one can only be certain about photon interactions. The actual quantum states of atoms are never observed directly. This is a XOR operation between two photons. Every other explanation is pure conjecture, a scientific leap of faith one might say.
Whydening Gyre
1 / 5 (2) Apr 22, 2013
okay, got it. Thanks, Anti.