How Will SPANGL4Q Impact Our Technology in the Future?

SPANGL4Q holds the promise of providing solutions to many key developments in quantum information technology. The QD spin-photon interfaces we will develop will be suitable for long-distance communications links over 105 km, with the possibility that the same photons may then be directly fed into integrated quantum chips, containing the interconnects for different qubit memories. From integrated quantum chips to long-distance communications, photons with the same wavelength may be used, and the differing technologies are compatible and feasible in existing telecom fibre networks. The first applications are likely to be in cryptography, where an absolutely secure “key” may be distributed. The first users are likely to be for government and banking applications, but one day, single photons may be routed down fibres to allow ultra-secure online banking and transactions for domestic users. The ultimate goals, the quantum computer and quantum internet, are further off, but represent as much of a breakthrough in computing capabilities as the standard integrated chip brought 40 years ago.

Ultra-long quantum memory spin-photon interfaces for ultra-long distances

The distance between the ground and a geostationary satellite is 36000km.


To allow quantum communications over very large distances (potentially across the globe) one will need to use satellite communications. The atmospheric attenuation of a direct link from the ground towards a satellite is the equivalent of just 5-8km horizontal distance on the ground. A single photon downlink from a low earth orbiting satellite has already been achieved, and a feasibility study by ESA has shown that the placement of an entangled pair source on a satellite is possible by 2014. A spin-photon interface with a quantum memory of >1s would prove invaluable for satellite communications as the time-of-flight to a geostationary satellite is of order ~0.2s. With a ground-based memory, one would be able to relay a signal via a satellite to any point on the globe, and set up a series of remotely entangled spins across the globe. Due to the reasonably high probability of loss, one needs to encode as much information on one photon as possible: for this reason, the plasmonic nanoantenna devices we will develop may be able to send may orders of angular momentum superpositions in a single photon. As well as their applications in cryptography and a future quantum internet, these sets of remotely entangled states would allow several fundamental tests of wavefunction collapse and relativity.

Quantum Memories for Integrated quantum photonic chips

A schematic of a waveguide circuit that may be used as a quantum processor

Quantum computing has several criteria, one of which is that it should be scalable. For this reason, integrated quantum photonic chips have recently gained much attention. However, to be efficient, the waveguides must eventually contain quantum memories. With the development of an electron spin – photon interface in a photonic crystal waveguide, one may integrate quantum memories into the architecture.

Technological impact of polarization-engineered nanophotonics

A major impact of SPANGL4Q will be that a much deeper understanding of polarization engineering of photonic structures will be developed that would have immediate applications in many other fields. For example, spintronics may be combined with photonics to allow spin-enabled data storage combined with high speed optoelectronic techniques. Another example is in imaging and molecular detection. Nanophotonic devices, in particular plasmonic nanoantennas are often suggested as a means to overcome the optical resolution limit for imaging. Polarization control in these structures would add an important element to their capabilities: for instance stereochemistry and DNA show sensitivity to circular polarization.