Abstract We evaluated a two-color two-photon entangled state generated in silicon via spontaneous four-wave mixing (SFWM) as a potential source for bosonic integrated circuits. Spatially entangled photon states were created using a pair of silicon waveguides that produced signal and idler photons through SFWM, allowing us to observe quantum interference between them. Assuming that the frequencies of the two-color photons were nearly identical, we characterized the generated quantum state by performing quantum state tomography on the bosonic system using a linear optical circuit. This study demonstrates the feasibility of using photon-pair sources generated in silicon via SFWM in bosonic optical circuits and highlights their potential for a wide range of applications in silicon-based optical quantum technologies.
Abstract We evaluated a two-color two-photon entangled state generated in silicon via spontaneous four-wave mixing (SFWM) as a potential source for bosonic integrated circuits. Spatially entangled photon states were created using a pair of silicon waveguides that produced signal and idler photons through SFWM, allowing us to observe quantum interference between them. Assuming that the frequencies of the two-color photons were nearly identical, we characterized the generated quantum state by performing quantum state tomography on the bosonic system using a linear optical circuit. This study demonstrates the feasibility of using photon-pair sources generated in silicon via SFWM in bosonic optical circuits and highlights their potential for a wide range of applications in silicon-based optical quantum technologies.
We evaluated a multi-color two-photon entangled state generated in silicon via spontaneous four-wave mixing (SFWM) as a potential source for bosonic integrated circuits. Spatially entangled photon states were created using a pair of silicon waveguides that produced signal and idler photons through SFWM, allowing us to observe quantum interference between them. Assuming that the frequencies of the multi-color photons were nearly identical, we characterized the generated quantum state by performing quantum state tomography on the bosonic system using a linear optical circuit. This study demonstrates the feasibility of using photon-pair sources generated in silicon via SFWM in bosonic optical circuits and highlights their potential for a wide range of applications in silicon-based optical quantum technologies.
Entangled photon pair generation is an important technology for realizing quantum information systems. Among various entangled photon pair sources, a source based on spontaneous four-wave mixing (SFWM) in a silicon wire waveguide (SWW) is now drawing attention. Thanks to the very large third-order nonlinearity in an SWW, we can realize highly efficient SFWM in a short ( ~ 1 cm) waveguide, which will possibly lead to an integrated entanglement source on a silicon chip. In this paper, we review recent progress on SWW-based entanglement sources. This study reviews the basic theory of SFWM, and then describes correlated and entangled photon generation experiments using SWWs and applications to quantum information experiments.
Silicon quantum photonics promises to take quantum optics to the large scale, where single photons carry the quantum information which can accelerate difficult computational problems, provide perfectly secure communication, or allow high-accuracy measurements. The silicon photonics platform offers miniature, high-yield, and high-performance photonics which are integrable with CMOS electronics and telecommunications-band optics. To date, only non-scalable photon-pair sources, based on spontaneous four-wave mixing (SFWM) in straight silicon waveguides have been shown to interfere [1]. Until now, single-photon experiments in silicon [2] have exclusively used an off-chip apparatus, such as a silica arrayed waveguide grating, to control and manipulate photon frequency. We present a silicon-on-insulator quantum photonic device (Fig. 1a) able to generate and analyse two maximally entangled qubits. We use this device to demonstrate high-visibility quantum interferencebetween resonant SFWM sources (analogous to [1]), phase-stable frequency-selection, and quantum state tomography. We varied the phase  to obtain the fringes shown in Fig. 1b, with a visibility of 96.8%. This high visibility indicates that the two microring sources are substantially identical. We setup the entangled state via the on-chip 17-dB extinction filters, and used quantum state tomography to analyse it (Fig. 1c). We measured a fidelity of 0.8. This is the first time an entangled state of photonic qubits has been both generated and analysed on-chip, and this generation has been done in a way which is scalable to larger photon number. These results represent a new step towards fully silicon-integrated quantum photonics.
A silicon quantum photonic circuit was proposed and demonstrated as an integrated quantum light source for telecom band polarization entangled Bell state generation and dynamical manipulation. Biphoton states were firstly generated in four silicon waveguides by spontaneous four wave mixing. They were transformed to polarization entangled Bell states through on-chip quantum interference and quantum superposition, and then coupled to optical fibers. The property of polarization entanglement in generated photon pairs was demonstrated by two-photon interferences under two non-orthogonal polarization bases. The output state could be dynamically switched between two polarization entangled Bell states, which was demonstrated by the experiment of simplified Bell state measurement. The experiment results indicate that its manipulation speed supported a modulation rate of several tens kHz, showing its potential on applications of quantum communication and quantum information processing requiring dynamical quantum entangled Bell state control.
Quantum mechanically, multiple particles can jointly be in a coherent superposition of two or more different states at the same time. This property is called quantum entanglement, and gives rise to characteristic nonlocal interference and stays at the heart of quantum information process. Here, rather than interference of different intrinsic properties of particles, we experimentally demonstrated coherent superposition of two different birthplaces of a four-photon state. The quantum state is created in four probabilistic photon-pair sources, two combinations of which can create photon quadruplets. Coherent elimination and revival of distributed 4-photons can be fully controlled by tuning a phase. The stringent coherence requirements are met by using a silicon-based integrated photonic chip that contains four spiral waveguides for producing photon pairs via spontaneous four-wave mixing. The experiment gives rise to peculiar nonlocal phenomena without any obvious involvement of entanglement. Besides several potential applications that exploit the new on-chip technology, it opens up the possibility for fundamental studies on nonlocality with spatially separated locations.
In this talk, I will discuss two applications of nonlinear quantum photonics in silicon nanowires: correlated photon pair sources and a single-photon wavelength converter. Correlated photon pairs can be generated in a nonlinear silicon waveguide through the spontaneous four-wave mixing (SFWM) process, where two photons from a bright pump laser are annihilated, and a two photons are spontaneously created at different wavelengths (the signal and idler). However, indistinguishable photon pairs are of particular interest for two-photon interference experiments, meaning that the signal and idler should have the same wavelength and be entirely identical to each other. Indistinguishable pairs can be generated with the SFWM process. where two pump lasers create a degenerate signal and idler at the frequency mid-way between them. Since the two photons are indistinguishable, it is not trivial to divide them into separate waveguides so as to manipulate them individually. I will present recent results concerning a silicon quantum splitter, where degenerate pairs are created in a ring resonator which is pumped in both directions. The ring is coupled to a sagnac loop interferometer, which combines the two directions at a 50 : 50 coupler. Here, a quantum interference effect (reverse-Hong Ou Mandel interference) splits the photons to two output waveguides. This device is ultra-compact and the use of a sagnac loop means that the phase is automatically set correctly for the interference. I will also discuss progress on single photon wavelength conversion in silicon nanowires using the four-wave mixing Bragg scattering (FWMBS) process. Here, two intense pump beams are used to modulate a weak signal, causing it to shift to the idler by the frequency difference between the pumps. In principle, this can allow coherent, noiseless frequency conversion of single photon signals. Fig. 1(b) shows output spectra from a 6mm silicon nanowire when the frequency shift is varied 100 GHz to 400 GHz. Multiple peaks are visible, corresponding to up-conversion and down-conversion of the input signal.