Control over the joint spectral amplitude of a photon pair has proved highly desirable for many quantum applications, since it contains the spectral quantum correlations, and has crucial effects on the indistinguishability of photons, as well as promising emerging applications involving complex quantum functions and frequency encoding of qudits. Until today, this has been achieved by engineering a single degree of freedom, either by custom poling nonlinear crystal or by shaping the pump pulse. We present a combined approach where two degrees of freedom, the phase-matching function, and the pump spectrum, are controlled. This approach enables the two-dimensional control of the joint spectral amplitude, generating a variety of spectrally encoded quantum states - including frequency uncorrelated states, frequency-bin Bell states, and biphoton qudit states. In addition, the joint spectral amplitude is controlled by photon bunching and anti-bunching, reflecting the symmetry of the phase-matching function.
Control over the joint spectral amplitude of a photon pair has proved highly desirable for many quantum applications, since it contains the spectral quantum correlations, and has crucial effects on the indistinguishability of photons, as well as promising emerging applications involving complex quantum functions and frequency encoding of qudits. Until today, this has been achieved by engineering a single degree of freedom, either by custom poling nonlinear crystal or by shaping the pump pulse. We present a combined approach where two degrees of freedom, the phase-matching function, and the pump spectrum, are controlled. This approach enables the two-dimensional control of the joint spectral amplitude, generating a variety of spectrally encoded quantum states - including frequency uncorrelated states, frequency-bin Bell states, and biphoton qudit states. In addition, the joint spectral amplitude is controlled by photon bunching and anti-bunching, reflecting the symmetry of the phase-matching function.
We investigate into experimentally detectable effects such as the Hong-Ou-Mandel (HOM) bunching and antibunching. These regimes can be characterized using the symmetry degree parameter DS that enters the two-photon coincidence probability P2c=(1−DS)/2. In the case of HOM bunching (antibunching), DS is positive (negative). Though the symmetry degree can generally be expressed in terms of the difference between the contributions coming from the symmetric and antisymmetric parts of the biphoton joint spectral amplitude (JSA), ψ(ω1,ω2), for a certain physically realizable class of the JSA, where ψ(ω1,ω2) is proportional to the product of amplitudes φ1(ω1)φ2(ω2) multiplied by a Gaussian shaped entangling factor, we find the sign of DS is primarily governed by the parity properties of the spectral function, φ12(ω)=φ1(ω)φ2∗(ω). It is the even (odd) part of φ12=φ12(+)+φ12(−) that meets the parity condition φ12(+)(ω−Ω)=φ12(+)(Ω−ω) (φ12(−)(ω−Ω)=−φ12(−)(Ω−ω)) to yield the positive (negative) contribution, DS(+) (−DS(−)), to the symmetry degree parameter: DS=DS(+)−DS(−). We have shown that switching between the bunching and antibunching regimes can be realized using the experimentally accessible family of modulated biphoton states produced using the spectral phase modulation fine-tuned via the sub-nanometer scale variation of the path length. For this class of modulated states, the Schmidt number has been computed as a function of the modulation parameter. This dependence reveals the structure of narrow resonance peaks strongly correlated with the corresponding narrow dips of the symmetry degree where the HOM antibunching occurs.
Photon pairs produced by the pulse-pumped nonlinear parametric processes have been a workhorse of quantum information science (QIS). Engineering the spectral property of quantum states is crucial for practical QIS applications. However, photon pairs with desirable spectral properties are currently achieved with specially engineered optical hardware but with severely limited flexibility in tuning the spectral properties of the sources. Here, we demonstrate a spectrally programmable photon pair source by exploiting a two-stage nonlinear interferometer scheme with a computer-controlled phase device. The phase-control device can introduce phase shifts for spectral engineering by a programmable phase function that can be arbitrarily defined. When the phase function is properly designed, the output spectrum of the source can be freely customized and changed without replacing any hardware component in the system. Using this approach, we are able to program photon pairs with factorable positively correlated and negatively correlated spectra. In addition, we also realize a source of multi-dimensional three-channel spectrally factorable photon pairs. Our investigation provides a flexible and powerful new approach for engineering the mode profile of photon pairs and should find wide applications in QIS.
Photon-pair states, whether spectrally correlated or separable, can all be very useful in quantum technology applications. For example, the former are used for improving the security of quantum key distribution, whilst the latter are the backbone in heralded single photon sources. It has been shown that the amount of spectral correlations is well-described by the shape of the Joint Spectral Amplitude function (JSA), which mostly depends on the relative group velocity relation between the pump, signal and idler photons within the source medium [1].
We present our results on the generation and manipulation of high dimensional quantum frequency states of light generated with AlGaAs chips working in the telecom band at room temperature. In the case of devices based on a collinear phase matching scheme we propose a method to generate and control the symmetry of broadband biphoton frequency combs, exploiting the interplay of cavity effects and relative temporal delay between the two photons of each pair. In the case of devices based on a transverse pump configuration we demonstrate that engineering the spatial properties of the pump beam allows to produce frequency-anticorrelated, correlated and separable states, and to control the parity of the biphoton wavefunction to induce either bosonic or fermionic particle statistics. These results open promising perspectives for communication and computation protocols exploiting high-dimensional quantum states, as well as for the quantum simulation of fermionic problems with photons on an integrated platform.
Single photons provide a natural platform for quantum communication and quantum networking, as they can be entangled in many degrees of freedom and maintain coherence over long-distance links. However, while their minimal interactions with the environment isolate them from detrimental noise, it can make them difficult to measure and manipulate. In particular, manipulation on the ultrafast timescale is necessary to fully exploit the energy-time (or spectral) photonic degree of freedom. Full control over the spectral properties of single photons is key to many quantum technologies and opens the door to natural high-dimensional quantum encodings. \n \nIn this thesis, we theoretically and experimentally examine the use of nonlinear optical processes mediated by strong laser pulses as a method to control the spectral properties of ultrafast single photons. By mixing single-photon pulses with strong escort pulses that have been shaped through dispersion in a nonlinear crystal, the shape of the escort is imprinted on the photon, resulting in a custom-tailored upconverted pulse. We theoretically examine this process for quadratic spectral phases and show that it has the potential to be simultaneously effective and efficient for the customization of single-photon spectral waveforms, and can be performed in an entanglement-conserving manner. \n \nWe then experimentally demonstrate the range of this technique through three applications. First, we show that sum-frequency generation with shaped pulses can be used to coherently measure time-bin encoded photons with bin separations on the order of picoseconds, well below the timing resolution of our detectors. Secondly, we show that this technique can be adapted to convert a train of pulses to a frequency comb, which can be read out in a straightforward manner using diffraction-based spectrometry. We also show here that this process can be performed in a polarization-maintaining fashion, and demonstrate that entanglement with a partner photon is conserved with high fidelity. Finally, we show that this process can be viewed as a time lens, which modulates a temporal waveform in an analogous fashion to a lens focusing a beam of light. We apply the time lens to a photon from an energy-time entangled pair, and show negative magnification of the joint spectrum through a reversal of the spectral correlations. Such processes could find application in quantum state engineering and high-speed single-photon measurement.
One 01 the main objectives of quantum optiCS is to prepare quantum light sources 'Nith the characteristics required lor various quantum optica ppllcallons. Pure single photons and entangled paired photons are two of the most 'Nidely used types of quantum tight. Single photons In a pure, well ellned quantum state may prove to be the building blocks lor future quantum technologies. These technologies promise enormous improvements ove heir ctasslcal counterparts In terms of speed or security. For eICample, in quantum inlormation processing, single photons may be used in quanturT ogic gales, playing the role of electrons in current electric circuits. Although light is all around us In all possible colors, polarizations and intensities, it I ICtremely difficult to get a single photon In a pure quantum state. On the other hand, 11 is relallvely easy to produce pairs of photons, and pure singl horons can be obtained from a two-photon source in a heralded way. Thus, generatlng paired photons with desired photonic properties becomes o'nE pf the cruciattasks in the research area 01 quantum optics and related applications.
rrhe process of spontaneous parametric down-conversion (SPDC) is one 01 the most convenient ways to produce pairs 01 photons. In SPDC, a strons ump laser beam Is shone on a nonlinear crystal. Occasionally, a pump photon disappears and two new photons with lower energy are create imultaneously. The production of photon paIrs In the nonlinear crystal is probabilistic and the fact that the two photons are produced simultaneously I n advantage. The two photons can be taken apart and one 01 them can be used as a trigger 10 indicate (herald) the presence of the olher, thereb elllng us when a photon is ready to be used. These pairs of photons have special types 01 correlation In their color (frequency), in theIr spatial shape ndIor In Iheir polarization. For many applications, such as quantum cryptography, these types of correlation may be useful, but at the moment 0 enerating pure Single photons they are detrimental since they diminish the purity of the single photon.
In this thesis, we are interested in the frequency properties 01 SPDC pairs of photons. and our main goal Is 10 demonstrate new methods 10 contre hese properties. The frequency properties ollhe photon pairs are described by its joint spectrum, which contains the information of the bandwidth, th wavalorm and the type of frequency correlation possessed by the two photons.
n the first part of our work, two new toolklts are added to the current toolbox to manipulate the joint spectrum of photon pairs. One tool is called pulse ronHill' technique. This technique is based on the appropriate Introduction of angular dispersion into the interacting waves. The feasibitity of thi method is demonstrated by observing a sevenfold increase of the band;dth of photon pairs. The corresponding experiment has been accomplished b dding angular dispersion into a coItinear SPDC geometry, where the interacting waves propagate at the same direction. Also, we discuss Ih mplicalion 01 this method lor the generation 01 narrow temporal Fourier transform limited btphotons, and paired photons 'Nith high degree 0 ntangtement. The second tool is called spatial-to·spectral' mapping technique. This technique takes eHec! in a noncoUinear geomelry, in which caSE he pump beam and the down-<:onverted paired photons propagate at different directions. With this situatton, the spatial features of the pump beam 'Nil ~ Imprinted inlo the lrequency distribution 01 the new created photon pairs. We eICperimenlalty prove this method by shaping the waveform, and tunin he types ollrequency correlation 01 the dO'M'l-converted two photons.
n addition, we propose a new scheme to fully control the Joint spectrum ollhe pholon pairs by combining the above two discussed techniques. In thi proposal, angular dispersion is introduced into a noncollinear SPDC geometry. This opens a new way to obtain pure single photons 'Nith tunabl band'Nidth.
Another topic discussed in this thesis is the exploration of more compact quantum light sources 'Nith versatile characteristics. We describe an SPDC !WO-photon source by using Brag9 reflection wavegulde (BAW) in AI .Gah. As material as down-converting material. Here, the nonlinear proces happens between a pump beam in 8 Bragg refleclion wavegulde mode, and down-converted photon pairs in total internal rellection (TtA) mode. Th ~aveguide dispersion properties can be largely modified by implementing different ridge sizes. and this allows the described monolithic source 10 oHe Ignificant control over the process band'Nidth. We numerically demonstrate the possibility 01 tuning the bandwidth 01 the photon pairs between 1 n~ nd 450 nm with the same waler structure. The results presented in this part have been obtained as a result 01 the collaboration ;th Prol. Amr S.
Helmy and his PhD student Payam Abolghasem from University of Toronto. In particular, the programs used lor the presented simulations have bee developed by the University of Toronto leam.
o summarize, In this thesis, we add new elements to the current ways 01 engineering quantum light sources. Two readily be used methods to enginee he spectrum of the photon pairs are presented. Particularly, new routes are provided to get pure heralded single photons and narrow tempora biphoton. In addil!on, a compact monolithic two-photon source ;th tunable bandwidth control Is Investigated, which could be very promIsing for furthe pOrlormance of various quantum applications towards reality.
Uoc I data Barcelona, 2009·11-16 Signature