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On Chip squeezed light sources for highly accurate Quantum navigation sensors and quantum key distribution.

GPS hacking and spoofing have made headlines around the world in recent years, from researchers successfully hacking a yacht’s navigation to bring it off its programmed course to the discovery of dozens of Russian ships whose GPS signals indicated they were on land when they were in fact out on sea.


Quantum sensing also provides a solution to security breaches. Unlike GPS platforms, quantum-enhanced navigation instruments do not rely on satellites to work, which makes them less vulnerable to hacking or spoofing – when a location falsely masquerades as something else. “As such, there is an urgency to develop and understand the defence capabilities of these rapidly evolving quantum technologies,” Helmy said.


The sensitivity of optical sensors and measurement devices is limited by technical noise sources like laser noise or by quantum noise, so-called shot noise. While the former can be eliminated for instance by implementing better – shot noise limited – lasers and by decoupling the measurement from the environment, shot noise is a fundamental property of the employed laser light imposed by quantum mechanics.


To achieve better signal-to-noise ratios the power used in the optical sensors and measurement devices can be increased. However, e.g. biological samples, investigated in an optical measurement device, are disturbed and eventually destroyed by laser light, which limits the amount that can be used.In integrated sensors also optical absorption and photo refractive effects limit the amount of laser power.


Researchers have used Squeezed light as a tool for high precision measurements as well as a tool for quantum information tasks like quantum key distribution.The word ‘squeezed’ describes a property of the light’s quantum noise. A squeezed-light laser beam shows less quantum noise than a conventional laser beam, even less quantum noise than a ‘laser beam’ having no photons at all. In this case, the light beam also shows a reduced (squeezed) fluctuation of its power, which is a useful property for optical measuring devices as well as for optical communication. ‘Squeezing’ of light is strongly linked to entanglement. Splitting squeezed light on beam splitter results in two output beams in an entangled state.


Additionally, advances in fabrication techniques have enabled ultra-low losses and ultra-high quality factors in these planar CMOS compatible materials such as silica and silicon nitride.


Squeezed light sensors

Quadrature squeezed light is a quantum state of light that exhibits noise properties which show in comparison to shot-noise a reduced amount of noise in one of the quadratures of the light field, and according the Heisenberg’s uncertainty relation, an increased amount in the orthogonal quadrature. This opens the possibility to employ such states in for instance interferometric measurements where the phase of the light is the quantity of interest.


While squeezed light can improve the signal-to-noise ratio of the measurement without increasing the laser power, state-of-the-art setups to generate the quantum states usually are bulky and, thus, incompatible with state-of-the-art integrated photonics.


Using Silicon photonics photon correlations and intensity correlations, respectively, have been observed. On-chip quadrature squeezed light has so far only been observed in Lithium Niobate waveguides as well as by utilization of the ponderomotive effect of a cryogenically cooled microoscillator in an optical cavity enabled by radiation pressure forces.


Researchers from Technical University of Denmark, Department of Physics, have designed a chip fabricated in Silicon Nitride using standardized lab processes which will enable room-temperature generation of quadrature squeezed light by the nonlinear optical Kerr effect.


Integration of quantum optical processes requires the host material to possess both a strong nonlinearity, essential for implementing high-efficiency parametric interactions, and low material and structural loss in order to preserve the generally fragile quantum states. These requirements are met by LPCVD amorphous stoichiometric silicon nitride (Si3N4).


“We anticipate an on-chip source for quadrature squeezed light to become a indispensable tool in integrated quantum photonics, e.g. for biological measurements, but also for quantum information tasks,” said the authors.



New quantum technology to counteract GPS hacking

As GPS or Global Positioning System is getting vulnerable to hacking, US engineers are working to harness quantum sensing technology to reduce current reliance on the world’s most ubiquitous navigation technology and introduce a more secure, accurate approach to mapping and navigation.


GPS’ vulnerability to hacking exposes potentially dangerous security risks in critical systems, from air traffic control to satellite communications. “Quantum sensing technology introduces groundbreaking approaches to measuring things,” Amr Helmy, Professor at the University of Toronto in Canada, said in a statement.


“It’s an exciting time because it’s a challenging time. But there are emerging needs in both instrumentation technologies and in security where quantum sensing is the answer,” he added.


Quantum sensors have capabilities that extend beyond the reach of conventional systems of measurement: they rely on the “squeezing effect”, whereby photons have the uncertainty inherent to their attributes minimized to precisely measure the position of a location.


To develop new navigation tools, Helmy is planning to integrate chip-based sources of quantum-squeezed light into existing optical gyroscopes. In addition to improving mapping accuracy, he points out that there are also situations in which a GPS would not be functional, “such as under water or at the North or South Poles. Quantum technology helps with that as well”.




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