Abstract-Terahertz quantum cryptography

Carlo Ottaviani, Matthew J. Woolley, Misha Erementchouk, John F. Federici, Pinaki Mazumder, Stefano Pirandola, Christian Weedbrook

https://arxiv.org/abs/1805.03514

A well-known empirical rule for the demand of wireless communication systems is that of Edholm's law of bandwidth. It states that the demand for bandwidth in wireless short-range communications doubles every 18 months. With the growing demand for bandwidth and the decreasing cell size of wireless systems, terahertz (THz) communication systems are expected to become increasingly important in modern day applications. With this expectation comes the need for protecting users' privacy and security in the best way possible. With that in mind, we show that quantum key distribution can operate in the THz regime and we derive the relevant secret key rates against realistic collective attacks. In the extended THz range (from 0.1 to 50 THz), we find that below 1 THz, the main detrimental factor is thermal noise, while at higher frequencies it is atmospheric absorption. Our results show that high-rate THz quantum cryptography is possible over distances varying from a few meters using direct reconciliation, to about 220m via reverse reconciliation. We also give a specific example of the physical hardware and architecture that could be used to realize our THz quantum key distribution scheme.

OT-New research signals big future for quantum radar

http://phys.org/news/2015-02-big-future-quantum-radar.html

A prototype quantum radar that has the potential to detect objects which are invisible to conventional systems has been developed by an international research team led by a quantum information scientist at the University of York.
The new breed of radar is a hybrid system that uses quantum correlation between microwave and optical beams to detect objects of low reflectivity such as cancer cells or aircraft with a stealth capability. Because the quantum radar operates at much lower energies than conventional systems, it has the long-term potential for a range of applications in biomedicine including non-invasive NMR scans.

The research team led by Dr Stefano Pirandola, of the University's Department of Computer Science and the York Centre for Quantum Technologies, found that a special converter - a double-cavity device that couples the microwave beam to an optical beam using a nano-mechanical oscillator - was the key to the new system.

The device can either generate microwave-optical entanglement (during the signal emission) or convert a microwave into an optical beam (during the collection of the reflection beams from the object). The research is published in Physical Review Letters.

A conventional radar antenna emits a microwave to scan a region of space. Any target object would reflect the signal to the source but objects of low reflectivity immersed in regions with high background noise are difficult to spot using classical radar systems. In contrast, quantum radars operate more effectively and exploit quantum entanglement to enhance their sensitivity to detect small signal reflections from very noisy regions.

Dr Pirandola said that while quantum radars were some way off, they would have superior performance especially at the low-photon regime.

"Such a non-invasive property is particularly important for short-range biomedical applications. In the long-term, the scheme could be operated at short distances to detect the presence of defects in biological samples or human tissues in a completely non-invasive fashion, thanks to the use of a low number of quantum-correlated photons.

"Our method could be used to develop non-invasive NMR spectroscopy of fragile proteins and nucleic acids. In medicine, these techniques could potentially be applied to magnetic resonance imaging, with the aim of reducing the radiation dose absorbed by patients."

 Explore further: Remote quantum applications, teleportation enabled by calling long distance between superconducting qubits

Journal reference: Physical Review Letters 

Read more at: http://phys.org/news/2015-02-big-future-quantum-radar.html#jCp