Photonics + Nonlinear optical crystals = Quantum computing at room temp

Read an article the other day in ScienceDaily (Path to quantum computing at room temp) which was reporting on a Phys.Org article (Researchers see path to quantum computing at room temp). Both articles were discussing recent research documented in a Physical Review Letters (Controlled-Phase Gate Using Dynamically Coupled Cavities and Optical Nonlinearities, behind paywall) being done at the Army Research Laboratory, Army and MIT researchers used photonis circuits and non-linear optical (NLO) crystals to provide quantum entanglement between photon waves. I found a pre-print version of the paper on, (Controlled-Phase Gate Using Dynamically Coupled Cavities and Optical Nonlinearities).

NLO Crystals

Nonlinear optics (source: Wikipedia Nonlinear Optics article) uses NLO crystals whicht when exposed to high electrical fields and high intensity light can modify or modulate light polarization, frequency, phase and path. For example:

Comparison of a phase-conjugate mirror with a conventional mirror. With the phase-conjugate mirror the image is not deformed when passing through an aberrating element twice.
  • Double or tripling light frequency, where one can double or triple the frequency of light (with two [or three] photons destroyed and a new one created).
  • Cross phase modulation where the wavelength phase of one photon can affect the wavelength phase of another photon.
  • Cross polarization wave generation where the polarization vector of a photon can be changed to be perpendicular to the original photon.
  • Phase conjugation mirror where light beams interact to exactly reverse “the propagation direction and phase variability” of a beam of light.

The Wikipedia article discusses a dozen more affects like this that NLO crystals can have on photons.

Quantum photon traps using NLO

MIT and Army researchers have theorized that there is another NLO crystal affect which can create a quantum photon trap. The researchers believe they can engineer a NLO crystal cavity(s) that act as a photon trap. With such an NLO crystal and photonics circuits, the traps could have the value of either a photon inside or a photon not inside the trap, but as it’s a quantum photon trap, it takes on both values at the same time.

Using photon trap NLO crystals, the researchers believe these devices could serve as room temperature qubits and quantum (photonic) gates.

The researchers state that with recent advances in nano-fabrication and the development of ultra-confined NLO crystals, experimental demonstrations of the photonics qubits and quantum gates appear feasible.

Quantum computing today

As our blog readers mayrecall, quantum computers today can take on many approaches but they all require extremely cold temperatures (a few Kelvin) to work. Even at that temperature quantum computing today is extremely susceptible to noise and other interference.

A quantum computer based on photonics, NLO crystals and operations at room temperature would be much more energy efficient, have many more qubits and much less susceptible to noise. Such a quantum computer could result in quantum computing being as ubiquitous as GPUs, TPU/IPUs or FPGA computational resources today .

Ubiquitous quantum computing would turn over our world. Digital information security today depends on mathematics for key exchanges which are extremely hard to do with digital computers. Quantum computers with sufficient qubits have no difficulty with such mathematics. Block chain relies on similar technology, so that too would also be at risk.

Standards organizations are working on security based on quantum proof algorithms but to date, we have yet to see any descriptions, let alone implementations of any quantum proof security in any information security scheme.

If what the researchers propose, pans out, advances in photonic quantum computing could restart information security of our world.

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