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A Quantum Internet at the Speed of Light?




The realization of quantum networks is one of the major challenges of modern physics. Now, new research shows how high-quality photons can be generated from 'solid-state' chips, bringing us closer to the quantum 'internet'.The number of transistors on a microprocessor continues to double every two years, amazingly holding firm to a prediction by Intel co-founder Gordon Moore almost 50 years ago. If this is to continue, conceptual and technical advances harnessing the power of quantum mechanics in microchips will need to be investigated within the next decade.

"We are at the dawn of quantum-enabled technologies, and quantum computing is one of many thrilling possibilities," says Dr Mete Atature from University of Cambridge Department of Physics. "Our results in particular suggest that multiple distant qubits in a distributed quantum network can share a highly coherent and programmable photonic interconnect that is liberated from the detrimental properties of the chips. Consequently, the ability to generate quantum entanglement and perform quantum teleportation between distant quantum-dot spin qubits with very high fidelity is now only a matter of time."

Developing a distributed quantum network is one promising direction pursued by many researchers today. A variety of solid-state systems are currently being investigated as candidates for quantum bits of information, or qubits, as well as a number of approaches to quantum computing protocols, and the race is on for identifying the best combination.

One such qubit, a quantum dot, is made of semiconductor nanocrystals embedded in a chip and can be controlled electro-optically. Single photons will form an integral part of distributed quantum networks as flying qubits. First, they are the natural choice for quantum communication, as they carry information quickly and reliably across long distances. Second, they can take part in quantum logic operations, provided all the photons taking part are identical.

Unfortunately, the quality of photons generated from solid-state qubits, including quantum dots, can be low due to decoherence mechanisms within the materials. With each emitted photon being distinct from the others, developing a quantum photonic network faces a major roadblock.

Now, researchers from the Cavendish Laboratory at Cambridge University have implemented a novel technique to generate single photons with tailored properties from solid-state devices that are identical in quality to lasers.

As their photon source, the researchers built a semiconductor Schottky diode device containing individually addressable quantum dots. The transitions of quantum dots were used to generate single photons via resonance fluorescence – a technique demonstrated previously by the same team.

Under weak excitation, also known as the Heitler regime, the main contribution to photon generation is through elastic scattering. By operating in this way, photon decoherence can be avoided altogether. The researchers were able to quantify how similar these photons are to lasers in terms of coherence and waveform – it turned out they were identical.

"Our research has added the concepts of coherent photon shaping and generation to the toolbox of solid-state quantum photonics," said Atature who led the research. "We are now achieving a high-rate of single photons which are identical in quality to lasers with the further advantage of coherently programmable waveform - a significant paradigm shift to the conventional single photon generation via spontaneous decay."

There are already protocols proposed for quantum computing and communication which rely on this photon generation scheme, and this work can be extended to other single photon sources as well, such as single molecules, color centres in diamond and nanowires.

The Daily Galaxy via University of Cambridge


Good luck with that.

In case you haven't figured it out yet, the source of the so-called 'quantum entanglement' is not some pseudo-scientific mumbo-jumbo of magical instantaneous communication between quantum entangled pixies. It's in Pauli exclusion principle.

There isn't any kind of collapse of wavefunction, which magically produces definite (exclusive) quantum states of 'quantum entangled' particles. There is only uncertainty which of the electrons in an orbital, electrons holding mutually exclusive quantum states, was released from the atom by absorbing a photon, or likewise, which of the electrons moving from a higher orbital to the lower one produced a photon. What practical uses such uncertainty may have is beyond me. A random number generator? Like there's not enough of those already.

If Pauli exclusion principle is correct, and there's no reason to believe otherwise, you can have up to 16 'quantum entangled' particles a not a single one more.

Use Helium atom as a toy model and you should clearly see what 'quantum entanglement' is really about.

I'm wondering if this technology, or an extension of it, could be used for quantum communication.

The reason is that, in my novels, there exists a network of devices used to transfer among the various Worlds (that is, alternate timelines), and they connect to each other via a complex system of quantum entanglement. I'm curious to know whether the science behind that is sound, or a bit more "rubbery."

Of course, there's also good reason to hope for practical applications in quantum communication, such as the ability to communicate in real time with the next Mars probe or a future manned Mars mission.

Of course, there's also good reason to hope for practical applications in quantum communication, such as the ability to communicate in real time with the next Mars probe or a future manned Mars mission.

So far entanglement properties can't be used for transfer or communication devices. It doesn't work like that. Space here doesn't permit hundreds of pages of dissertation but so far, entanglement can't be used for communication for there are so many bazillions of bits of information involved in communication that the complexity is beyond comception that's involved here. It would be very NICE if we could communicate in practically zero time alright but entanglement isn't (so far) going to provide that. I'm not saying it won't in the future...transoceanic travel was thought to be impossible because you'd fall of the edge of the Earth. What is thought to be impossible one year is old hat the next often times but not always. Some things really ARE impossible, some things when understood, are not. It is so close to being impossible for me to find under my pillow tomorrow morning a 1 kilo gold bar that we can safely call it impossible "for all practical purposes". Now prove that possible and I'll split it with you!

The way I read it before, entanglement happens instantly, way way faster than C.

Electric charge already goes through conductors and semiconductors, thus operates a mother board at the speed of light or so very close, so what is gained by a chip that goes the speed of light

I think many are a bit confused on how a computer works. Now if nano scale can be further reduced and more transistors can be packed into the same space, then fine, that's what we already do now. The limit is the size of a metal atom or two to make a line of them, hence a conductor. We're approaching that now. Next step? An entirely new way to store memory and to remove most of electrical resistance so chips stay cooler and function more rapidly. The hotter a conductor is the more resistance it has which makes more heat which makes more resistance and so on. When distances become small enough to be an atom or two then that's the limit of efficiency with the chip tech we have now.

Such things as electron spin, DNA chips and mouse brains have been postulated with which to make a future generation of ccmputers, so when your super duper intelligent beyond belief computerized gorgeous voluptous jiggly smiley silicone love doll forty years from now asks you for a piece of cheeze and some newspaper to tear up into a nest, instead of a night out, dancing, a scrumptous Italian dinner and wine, don't be surprised.

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