Developing interferometers to detect electric field signals with very high sensitivity

The project is about developing interferometers to detect electric field signals with very high
sensitivity, beyond that enabled by classical mechanics. Specifically, it aims at increasing the
sensitivity of time-resolved infrared and terahertz field measurements.
Enhancement of interferometry in the past years has led to fundamental discoveries in numerous
fields, and this particular project can reveal new and revolutionary interactions to help us
widen our scope of reality and understand the nature of the universe a little better. The sensitivity of
interferometers can be boosted and overcome the standard-quantum limits by using entangled
photons or squeezed states. This was indeed one of the breakthroughs of the last 30 years of
research. One of the most remarkable examples of this possibility is described in the seminal work of Carlton Caves: "Quantum-mechanical noise in an interferometer" published in Physical Review D, 23,
1693 (1981).
We are currently limited to visible and near-infrared frequencies, and this project will be about using
these quantum states to increase the sensitivity of low-frequency radiation, in the infrared and THz
part of the spectrum. Delving into this largely unexplored part of the spectrum will provide exciting
research challenges, on top of potentially relevant technological outcomes. At terahertz frequency,
unusual light-matter interactions can be observed, such as non-perturbative effects of carriers
tunnelling, which complements some intriguing applications including security and quality control.
The project goal is that of increasing the sensitivity of infrared and THz detectors using quantum
states of light. The primary approach for infrared sensing that will be investigated is known as timedomain
spectroscopy. This is a detection technique that involves short laser pulses, in the order of
few tens of femtoseconds, which sample in time the unknown infrared radiation thanks to a
nonlinear process called electro-optical effect that occurs in certain nonlinear crystals. A detailed
account of this technique can be found in "Introduction to THz Wave Photonics", by X.-C. Zhang and
Jingzhou Xu (Springer 2009). More up to date research papers will complement this background.
The project aims at improving this approach by applying the recently developed quantum metrology
techniques. The starting point to understand why a quantum state can help to improve the
sensitivity of a measurement is described in several textbooks, such as "Introduction to Quantum
Optics", by G. Grynberg, A. Aspect, and C. Fabre (Cambridge University Press, 2010).
The time-domain spectroscopy is, in essence, a pulsed interferometer. To enhance its sensitivity
above the standard quantum limit squeezed states will be injected into the open port of the
interferometer, following the original Caves' proposal. Such nonclassical state can be generated by
amplifying the vacuum fluctuations in a parametric amplifier pumped by femtosecond optical pulses.
Reference textbooks that are relevant to this background on nonlinear light-matter interaction are
Ultrashort Laser Pulse Phenomena, by J.-C. Diels and W. Rudolph (Academic Press, 2006) and
Nonlinear Optics, by R. Boyd (Academic Press, 2008).
Overall, the project aims at developing new, table-top technologies to improve the sensitivity of
effects that occur at the femtosecond and picosecond time scales. The implications of developing
Electronics and Nanoscale Engineering Research Proposal
this technology and advancing the field of photonics are massive, and as a result, there are a number
of topics which branch off from this field which provide numerous promising technological and
industrial ventures which could revolutionise modern day society if they were to come to fruition.
For instance, other time-varying effects could be investigated, such as those associated with weak
magnetic fields, or perturbations of the local gravity.