Abstract
For fundamental tests of quantum physics as well as for quantum communications non-classical states of light are an important tool. In our research we focus on developing semiconductor-based and integrated sources of single photons and entangled photon pairs.
In this talk, we will give a survey of quantum algorithms based on quantum walks, focusing in particular on search algorithms. The father of almost all quantum search algorithms is Grover's algorithm, which can be seen as a quantum walk on the complete graph. Later on, variations of Grover's algorithm have been proposed for searching on other graphs, such as the grid or the hypercube.
In theory, quantum key distribution (QKD) provides information-theoretic security based on the laws of physics. Owing to the imperfections of real-life implementations, however, there is a big gap between the theory and practice of QKD. This gap has been recently exploited by several quantum hacking activities.
In practical applications of communication schemes it is often necessary to amplify the transmitted signals. Because of the intrinsic noise due to Heisenberg's uncertainty principle, a quantum signal requires an amplification process which is different than the one used for classical signals.
Digital signatures ensure that messages cannot be forged or tampered with. They are widely used to provide security for electronic communications, for example in financial transactions and electronic mail. Importantly, signed messages are also transferrable, meaning that if one recipient accepts a message as genuine, then she is guaranteed that others will also accept the same message if it is forwarded.
As a standard method for producing correlated photon pairs (biphotons), spontaneous parametric down-conversion in nonlinear crystal usually has a wide bandwidth (terahertz) and very short coherence time (pico-seconds). Within spontaneous four-wave mixing process in cold atom ensembles, here we present a method for producing narrow-band (megahertz) Stokes and anti-Stokes paired photons.
The conventional electronic devices such as personal computer and mobile phones are primarily based on the control of electron charge in semiconductors. Although the tremendous progress in micro-fabrication technologies has accelerated the miniaturization of electronic devices, the size of devices will soon encounter the fundamental physical limits of that miniaturization. Further scale reduction beyond these limits will require a radical alteration of the concept of functional devices.
