FOCUS BUSINESS & RESEARCH NEWS
FOCUS BUSINESS &
A
new type of quantum holography that uses entangled photons to overcome the limitations of conventional
holographic approaches could lead to improved medical imaging and speed the advance of quantum information science. A team of physicists from the University of
Glasgow say they are the first to find a way to use quantum-entangled photons to encode information in a hologram. Holography is familiar to many from its use as security images printed on credit cards and passports, but it has many other practical applications, including data storage, medical imaging and defence. Classical holography creates two- dimensional renderings of three-dimensional objects with a beam of laser light split into two paths. The path of one beam, the object beam, illuminates the holograph’s subject, with the reflected light collected by a camera or special holographic film. The path of the second beam, the reference beam, is bounced from a mirror directly to the collection surface without touching the subject. The holograph is created by measuring the
differences in the light’s phase where the two beams meet. The phase is the amount the waves of the subject and object beams mingle and interfere with each other, a process enabled by the light property ‘coherence’.
Harnessing quantum entanglement The Glasgow team’s quantum holography process also uses a beam of laser light split into two paths, but unlike in classical holography, the beams are never reunited. Instead, the process harnesses the unique properties of quantum entanglement – a process Einstein famously called ‘spooky action at a distance’ – to gather the coherence information required to construct a holograph, even though the beams are forever parted. Their process begins in the lab by shining a blue laser through a special nonlinear crystal which splits the beam into two, creating entangled photons in the process. Entangled photons are intrinsically linked – when an agent acts on one photon, it’s partner is also affected, no matter how far apart they are. The
6 Electro Optics March 2021
RESEARCH NEWS Quantum holography technique set to advance imaging
The new development could help advance medical imaging to reveal finer cell details and more about how biology functions
photons in the team’s process are entangled in both their direction of travel and polarisation. Two streams of entangled photons are then
sent along different paths. One photon stream – the equivalent of the object beam in classical holography – is used to probe the thickness and polarisation response of a target object by measuring the deceleration of the photons as they pass through it. The waveform of light shifts to different degrees as it passes through the object, changing the phase of the light.
‘The process we’ve developed frees us from the limitations of classical coherence and ushers holography into the quantum realm’
Meanwhile, its entangled partner hits a
spatial light modulator, the equivalent of the reference beam. Spatial light modulators are optical devices which can fractionally slow the speed of light which passes through them. Once the photons pass through the modulator, they have a different phase compared to their entangled partners which have probed the target object. In standard holography, the two paths
would then be superimposed on each other, and the degree of phase interference between them would be used to generate a hologram on the camera. In the most striking aspect of the team’s quantum version of holography,
the photons never overlap with each other after passing through their respective targets. Instead, because the photons are entangled as a single ‘non-local’ particle, the phase shifts experienced by each photon individually are simultaneously shared by both. The interference phenomenon occurs
remotely, and a hologram is obtained by measuring correlations between the entangled photon positions using separate megapixel digital cameras. A high-quality phase image of the object is finally retrieved by combining four holograms measured for four different global phase shifts implemented by the spatial light modulator on one of the two photons.
Holography entering the quantum realm In the team’s experiment, phase patterns were reconstructed from artificial objects like the letters ‘UofG’ programmed on a liquid crystal display, but also from real objects such as a transparent tape, silicon oil droplets positioned on a microscope slide and a bird feather.
Lead author Dr Hugo Defienne, of the
university’s School of Physics and Astronomy, said: ‘Classical holography does very clever things with the direction, colour and polarisation of light, but it has limitations, such as interference from unwanted light sources and strong sensitivity to mechanical instabilities. ‘The process we’ve developed frees us
@electrooptics |
www.electrooptics.com
Shutterstock.com
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50
