February 27, 2017

More technical details about China's Quantum Radar claims and quantum radar lab work

In September 2016, there were claims from China that they had developed quantum radar. There has been recent articles discussing China's quantum radar

The quantum radar system was developed by the Intelligent Perception Technology Laboratory of the 14th Institute of CETC. Researchers completed experiments on quantum detection and target scattering characterization. In the target detection experiment, conducted in a real atmospheric environment, the detection ability of the system was proven to be over 100 kilometers (62 miles). If the claims are true then China can detect stealth planes at a range of 62 miles with accuracy sufficient for missile targeting. They would be able to create a detection network with quantum scanners spaced about 100 miles apart.

It had five times the “potential range” of a laboratory prototype jointly developed by researchers from Canada, Germany, Britain and the United States in 2015. DARPA has reportedly funded similar research and military suppliers such as Lockheed Martin are also developing quantum radar systems for combat purposes, according to media reports, but the progress of those military projects remains unknown.

According to a Sept. 8 report by Mingbao Daily, the theoretical basis of the quantum radar is that an object will change its quantum properties after receiving photonic signals. The quantum radar can easily detect stealth aircraft and is highly resistant to becoming jammed. Military experts have stated that once a stealth aircraft is located by the radar, it stands little chance to escape the strikes of air defense missiles.

Jamming would be noticable

Conventional radar can be jammed by transmitting ‘white noise’ on the same frequencies. Entangled photons retain their quantum link. Attempting to break that link would be a giveaway. And any attempt to distort the behavior would be equally noticeable.

Modern composites can ‘trap’ radio waves within their molecular structure, whatever happens to an entangled photon would be replicated — and measured — in its paired mate back at the radar site.

And different materials affect protons in different ways.

Because of this, analysts say quantum radar could ultimately be capable of determining what an aircraft is made of — or even carrying.

The 2015 and 2017 Work from Canadian, UK and American researchers

There has been scientific analysis around quantum radar

Arxiv - Quantum Illumination at the Microwave Wavelengths (15 pages)

Researchers assumed unit quantum efficiency for the optical part of their quantum receiver. This is not far from current experimental conditions: photon collection efficiencies from optical cavities can be very high (over 74% ), loss at the beam splitter can be extremely low, and photodetection can be extremely efficient at optical wavelengths. Thus the main source of loss may come from the optical storage of the idler mode, to be preserved during the signal roundtrip time. This is not an issue for short-range applications but, for long-range tasks, the idler loss must remain below 3 dB, otherwise the QI advantage of the phase-conjugating quantum receiver is lost. While using a good quantum memory (e.g., a rare-earth doped-crystal) would solve the problem, the practical solution of storing the idler into an optical-fiber delay line would restrict the maximum range of the quantum radar to about 11.25 km in free-space (assuming a fiber loss of 0.2 dB/km and fiber propagation speed equal to 2c/3, where c is vacuum light-speed).

Extending the results to lower frequencies (below 1 GHz), the scheme could potentially be used for noninvasive NMR spectroscopy in structural biology (structure of proteins and nucleic acids) and in medical applications (magnetic resonance imaging).

Future implementations of quantum illumination at the microwave regime could also be achieved by using other quantum sources, for instance based on Josephson parametric amplifiers, which are able to generate entangled microwave modes of high quality. These amplifiers might become a very good choice once that suitable high-performance microwave photo-detectors are made available.

A quantum radar device could detect microwave reflections that would normally be swamped by the noisy background radiation. It would contain two devices capable of interconverting visible light with microwaves, a capability that exists with current technology. First the top converter couples two entangled beams, a microwave one (red wavy line) and a visible one (red straight line); then the microwave reflection is converted to visible light that interferes with the initial visible beam in the detector.

Quantum entanglement scheme previously demonstrated for visible photons into the microwave regime could boost radar performance.

Arxiv - Quantum Estimation Methods for Quantum Illumination (revised Feb 27, 2017) (9 pages)

Quantum illumination consists in shining quantum light on a target region immersed in a bright thermal bath, with the aim of detecting the presence of a possible low-reflective object. If the signal is entangled with the receiver, then a suitable choice of the measurement offers a gain with respect to the optimal classical protocol employing coherent states. Here, we tackle this detection problem by using quantum estimation techniques to measure the reflectivity parameter of the object, showing an enhancement in the signal-to-noise ratio up to 3 dB with respect to the classical case when implementing only local measurements. Our approach employs the quantum Fisher information to provide an upper bound for the error probability, supplies the concrete estimator saturating the bound, and extends the quantum illumination protocol to non-Gaussian states. As an example, we show how Schrodinger's cat states may be used for quantum illumination.

Conclusions.— We have considered the problem of optimally estimating the reflectivity parameter of an object embedded in an environment. Our analysis shows that, using entangled states as a resource, we can obtain an advantage up to 3 dB in the QFI with respect the optimal classical strategy. We have applied these results to the QI scenario, providing a non-trivial upper bound on the optimal error probability. This bound depends solely on the QFI of the signal-idler state, which is easily computable, and it allows us to extend the advantage of the QI protocol to a class of non-Gaussian states. Moreover, our results are not limited to a bright environment (NB 1) and low signal photons (NS 1) cases, but they hold for any number of photons in the bath and the signal. In the examples, we have discussed the Gaussian states and the multilevel Schr¨odinger’s cat states, which also performs optimally in the low-photon regime. Indeed, recent technological advances show that Schr¨odinger’s cat states can be useful for quantum computation, and this makes of them a possible alternative to the Gaussian states in the QI protocol.

Single photon detectors claims to be heart of China's greater quantum radar efficiency

The CETC breakthrough benefited largely from the recent rapid development of single-photon detectors, which allowed researchers to capture returning photons with a high degree of efficiency.

CETC said the quantum radar’s advantage was not limited to the detection of stealth planes.

The field test had opened a “completely new area of research”, it said, with potential for the development of highly mobile and sensitive radar systems able to survive the most challenging combat engagements.

Quantum radar systems could be small and would be able to evade enemy countermeasures such anti-radar missiles because the ghostly quantum entanglement could not be traced, it said.

Short range radar can detect stealth aircraft but not with very good accuracy Traditional limitation of VHF and UHF-band radars is that their pulse width is long and they have a low pulse repetition frequency [PRF]—which means such systems are poor at accurately determining range. As Mike Pietrucha, a former Air Force an electronic warfare officer who flew on the McDonnell Douglas F-4G Wild Weasel and Boeing F-15E Strike Eagle once described to me, a pulse width of twenty microseconds yields a pulse that is roughly 19,600 ft long—range resolution is half the length of that pulse. That means that range can’t be determined accurately within 10,000 feet. Furthermore, two targets near one another can’t be distinguished as separate contacts.

Signal processing partially solved the range resolution problem as early as in the 1970s. The key is a process called frequency modulation on pulse, which is used to compress a radar pulse. The advantage of using pulse compression is that with a twenty-microsecond pulse, the range resolution is reduced to about 180 feet or so.

Quantum radar is based on the theory of quantum entanglement and the idea that two different particles can share a relationship with one another to the point that, by studying one particle, you can learn things about the other particle—which could be miles away. These two particles are said to be "entangled".

In quantum radars, a photon is split by a crystal into two entangled photons, a process known as "parametric down-conversion." The radar splits multiple photons into entangled pairs—and A and a B, so to speak. The radar systems sends one half of the pairs—the As—via microwave beam into the air. The other set, the Bs, remains at the radar base. By studying the photons retained at the radar base, the radar operators can tell what happens to the photons broadcast outward. Did they run into an object? How large was it? How fast was it traveling and in what direction? What does it look like?

Quantum radars defeat stealth by using subatomic particles, not radio waves. Subatomic particles don't care if an object's shape was designed to reduce a traditional, radio wave-based radar signature. Quantum radar would also ignore traditional radar jamming and spoofing methods such as radio-wave radar jammers and chaff.

Lockheed Martin had a patent related to quantum radar in 2008

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