"We can scarcely avoid the conclusion that light consists in the transverse undulations of the same medium which is the cause of electric and magnetic phenomena." - J. C. Maxwell (1862)or a particle:
"Nach der hier ins Auge zu fassenden Annahme ist bei Ausbreitung eines von einem Punkte ausgehenden Lichtstrahles die Energie nicht kontinuierlich auf größer und größer werdende Räume verteilt, sondern es besteht dieselbe aus einer endlichen Zahl von in Raumspunkten lokalisierten Energiequanten, welche sich bewegen, ohne sich zu teilen und nur als Ganze absorbiert und erzeugt werden können." - A. Einstein (1905) [Pardon?]it suddenly came to me ....
The photon is really a piece of quantum mechanics that accidentally fell into the middle of the 19-th century and some people just never managed to get over it.
We report on a spatio-temporal imager of normalized second order correlations g(2)(x′,t′,x,t) between photons. The imager is based on a monolithic 4 ×4 array of single-photon avalanche diodes implemented in CMOS technology and utilizes a simple algorithm to treat multiphoton time-of-arrival distributions. The chip, that enables 100 ps temporal resolution, incorporates integrated high-bandwidth electronics for off-chip processing, operating with photon fluxes as low as 10 photons per second at room-temperature. For any interval of observation, the imager yields a normalized correlation function g(2) calculated from photon arrivals at different detector pairs. The chip can be used to locally probe second-order correlations in the condensate and non-condensed fractions in experiments on transient BEC of cavity exciton polaritons.
We continue with our previous program where we introduced a set of quantum-based design rules directed at quantum engineers who design single-photon quantum communications and quantum imaging devices. Here, we report on experimental progress using SPAD (single photon avalanche diode) arrays of our design and fabricated in CMOS (complementary metal oxide semiconductor) technology. Emerging high-resolution imaging techniques based on SPAD arrays have proven useful in a variety of disciplines including bio-fluorescence microscopy and 3D vision systems. They have also been particularly successful for intra-chip optical communications implemented entirely in CMOS technology. More importantly for our purposes, a very low dark count allows SPADs to detect rare photon events with a high dynamic range and high signal-to-noise ratio. Our CMOS SPADs support multi-channel detection of photon arrivals with picosecond accuracy, several million times per second, due to a very short detection cycle. The tiny chip area means they are suitable for highly miniaturized quantum imaging devices and that is how we employ them in this paper. Our quantum path integral analysis of the Young-Afshar-Wheeler interferometer showed that Bohr's complementarity principle was not violated due the previously overlooked effect of photon bifurcation within the lens-a phenomenon consistent with our quantum design rules-which accounts for the loss of which-path information in the presence of interference. In this paper, we report on our progress toward the construction of quantitative design rules as well as some proposed tests for quantum imaging devices using entangled photon sources with our SPAD imager.
A common syndrome in much of the current quantum optics and quantum computing literature is the casual switching between classical concepts (e.g., geometric rays, electromagnetic waves) and quantum concepts (e.g., state vectors, projection operators). Such ambiguous language can confuse designers not well versed in the deeper subtleties of quantum mechanics, or worse, it can lead to a flawed analysis of new designs for quantum devices. To validate that a quantum device can be constructed with the expected characteristics and that its quantum effects are correctly interpreted, a set of unambiguous design rules would be useful. In this paper we enumerate such a set of easily applied quantum rules in the hope that they might facilitate clearer communication between researchers and system developers in the field. In part, we are motivated by recently reported interferometer results that have not only led to flawed claims about disproving fundamental quantum principles, but have elicited equally flawed counter arguments from supposedly knowledgeable respondents. After one hundred years of testing Einstein's photon, it is alarming that such widespread confusion still persists. Our proposed quantum design rules are presented in a practical diagrammatic style, demonstrating their effectiveness by analyzing several interferometers that have appeared in the recent literature. Application to other quantum devices e.g., the quantum eraser, are also discussed. We stress that these rules are entirely quantum in prescription, being particularly appropriate for single-photon devices. Classical optics concepts e.g., refractive index, are not required since they are subsumed by our quantum rules.
| Attribute | Dimension | Unit |
| HeNe laser wavelength (λ) | 650 | nm |
| Optical total path length | 5 | meters |
| Lens distance from pinholes | 4.2 | meters |
| Pinhole diameter | 0.25 | mm |
| Pinhole cen-2-cen spacing | 2 | mm |
| Aperture stop diameter | 20.8 | mm |
| Focusing lens diameter | 30 | mm |
| Lens focal length | 1000 | mm |
| Image cen-2-cen spacing | 0.6 | mm |
| Wire comb gauge (200 λ) | 127 | μm |
| Wire comb spacing (2000 λ) | 1.4 | mm |