This work is supported by the ERA-NET CHIST-ERA (&#8216;QScale&#8217; project) and by the ERC starting grant &#8216;HybridNet&#8217;. F. Barbosa acknowledges the support from CNR and FAPESP, and K. Huang the support from the Foundation for the Author of National Excellent Doctoral Dissertation of China (PY2012004) and the China Scholarship Council. C. Fabre and J. Laurat are members of the Institut Universitaire de France.

1. Optical Parametric Oscillator
<ol>
	<li>Build a 4&#160;cm long semimonolithic linear cavity (for improved mechanical stability and reduced intracavity losses). The input mirror is directly coated on one face of the nonlinear crystal.</li>
	<li>Choose an input coupler reflection of 95% for the pump at 532 nm and high-reflection for the signal and idler at 1,064 nm. Inversely, choose the output coupler to be highly reflective for the pump and of transmittance T=10% for the infrared. The free spectral range of the OPO is equal to &#916;&#969; = 4.3 GHz and the bandwidth is around 60 MHz. Make the cavity triply resonant, i.e. for the pump and for the down-converted fields.</li>
	<li>Use a KTP crystal for the type-II OPO system or a PPKTP crystal for the type-I OPO. Temperature-stabilize the crystals at their phase-matching temperatures.</li>
	<li>Use as laser source a continuous-wave frequency doubled Nd:YAG laser. Pump the OPO at 532 nm and use the infrared light, after spatial filtering by a high-finesse cavity (mode cleaner), as a local oscillator (LO) for the homodyne detection.</li>
	<li>Achieve the mode-matching between the pump and the cavity mode.</li>
	<li>Lock the cavity length on the pump resonance by the Pound&#8211;Drever&#8211;Hall technique. For this purpose, apply a 12 MHz electro-optic modulation to the pump and detect the light back-reflected from the cavity with an optical isolator.</li>
</ol>
2. Conditional Preparation: Filtering the Heralding Path
<ol>
	<li>Separate the OPO output into two modes. One corresponds to the heralding mode, while the other one is the heralded state that will be detected by the homodyne detection.</li>
	<li>Guide the heralding mode towards the single-photon detector. Specifically, for the type-II OPO, separate the orthogonal signal and idler modes by a polarized beam splitter (PBS). For the type-I OPO, tap out a small fraction (3%) of the squeezed vacuum by a beam splitter (BS).</li>
	<li>Filter the heralding mode to remove the frequency non-degenerate modes due to the OPO cavity. For an OPO, the output indeed contains many pairwise correlated but spectrally separated modes, &#969;0+n&#916;&#969; and &#969;0-n&#916;&#969; where n is an integer. To generate a heralded state at the carrier frequency, it is necessary to filter out all of these non-degenerate modes.
	<ol>
		<li>Use first an interferential filter with a bandwidth of 0.5 nm.</li>
		<li>Add a homemade linear Fabry&#8211;Perot cavity with a free spectral range of 330 GHz and a bandwidth of 300 MHz (length around 0.4 mm and finesse around 1,000). The cavity bandwidth is chosen to be larger than the one of the OPO and the free spectral range to be larger than the frequency window of the interferential filter.</li>
		<li>Achieve at least an overall 25 dB rejection of the non-degenerate modes.</li>
	</ol>
	</li>
	<li>Lock the filtering Fabry-Perot cavity by the dither-and-lock technique.
	<ol>
		<li>For this purpose, inject a backward propagating auxiliary beam via an optical switch and reject it at the entrance of the filtering cavity by an optical isolator. Detect the light at the output.</li>
		<li>Lock the cavity during 10 msec and start after the measurement period for 90 msec with the auxiliary-beam off.</li>
	</ol>
	</li>
	<li>Detect the filtered heralding mode by a single-photon detector during the measurement period. A superconducting single-photon detector (SSPD) is used to limit the amount of dark noise (few Hz), which otherwise would degrade the fidelity of the conditional state.</li>
</ol>
3. Quantum State Tomography by Homodyne Detection
<ol>
	<li>Detect the heralded state with a balanced homodyne detection composed of a 50/50 beam splitter where the field to characterize and a strong continuous-wave local oscillator (LO, 6 mW) are brought to interfere, and a pair of high quantum efficiency InGaAs photodiodes.</li>
	<li>In order to align the detection, inject into the OPO cavity a bright auxiliary beam at 1,064 nm and mode match this mode with the LO mode. Achieve a fringe visibility close to unity. Any mode mismatch quadratically translates into detection losses.</li>
	<li>Check the homodyne detection properties. With a LO power of 6 mW, the shot noise limit (SNL) is flat up to 50 MHz. It is more than 20 dB above the electronic noise at low analysis frequency (MHz), 16 dB above at the analysis frequency of 50 MHz. This distance is a critical parameter as it translates into losses in the detection (a 10 dB (20 dB) distance translates into a 10% (1%) effective loss)24.</li>
	<li>For every detection event from the single-photon detector, record the homodyne photocurrent with an oscilloscope with a sampling rate of 5 Gs/sec during 100 nsec. Sweep the LO phase with a PZT-mounted mirror during the measurement.</li>
	<li>Filter each recorded segment with a given temporal mode function to obtain at each successful preparation a single quadrature value of the conditional state. The optimal mode function for low gain is close to a double-sided exponential function25 with a decay constant equal to the inverse of the OPO bandwidth. The optimal mode can also be found by using a eigenfunction expansion of the autocorrelation function26.</li>
	<li>Accumulate measurements (50,000 are required for the tomography) and post-process the data with a maximum-likelihood algorithm27. This procedure enables reconstruction of the density matrix of the heralded state and the corresponding Wigner function8.</li>
</ol>
4. Conditional Preparation of Single Photon State with a Type-II OPO
<ol>
	<li>Pump the type-II OPO far below threshold (1 mW here for a 80 mW threshold) to have a very low probability of multiphoton pairs.</li>
</ol>
5. Conditional Preparation of Coherent State Superposition with a Type-I OPO
<ol>
	<li>Check the squeezed vacuum generated by the OPO close to threshold with a spectrum analyzer. The measured noise spectra are shown in Figure 3.</li>
	<li>Operate the OPO at a pump power enabling observation of around 3 dB of squeezing at low sideband frequencies (few MHz).</li>
	<li>In the homodyne measurement, the phase information is important for phase-dependent states such as the CSS state. Scan the LO phase with a 10 Hz sawtooth wave with a duty cycle of 90% (corresponding to the 90 msec of measurement period and 10 msec of locking period.) Synchronize the sweep to make sure that during the measurement period, there is a single one-directional sweep of the PZT-mounted mirror.</li>
	<li>Use the homodyne signal to measure the variance and then infer the phase of the measured quadrature.</li>
</ol>

<ol>
	<li>Dell'Anno, F., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Multiphoton+quantum+optics+and+quantum+state+engineering.">Multiphoton quantum optics and quantum state engineering.</a> Phys. Reports. 428, 53-168 (2006).</li><li>O'Brien, J. L., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Photonic+quantum+technologies.">Photonic quantum technologies.</a> Nature Photon. 3, 687-695 (2009).</li><li>Bachor, H. -. A., Ralph, T. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> A guide to experiments in quantum optics. , (2004).</li><li>Reid, M. D., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+Einstein-Podolsky-Rosen+paradox:+from+concepts+to+applications.">The Einstein-Podolsky-Rosen paradox: from concepts to applications.</a> Rev. Mod. Phys. 81, 1727-1751 (2009).</li><li>Van Loock, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Optical+hybrid+approaches+to+quantum+information.">Optical hybrid approaches to quantum information.</a> Laser &amp; Photonics Review. 5, 167-200 (2011).</li><li>Knill, E., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+scheme+for+efficient+quantum+computation+with+linear+optics.">A scheme for efficient quantum computation with linear optics.</a> Nature. 409, 46-52 (2001).</li><li>Ralph, T. C., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Quantum+computation+with+optical+coherent+states.">Quantum computation with optical coherent states.</a> Phys. Rev. A. 68, 042319 (2003).</li><li>Leonhardt, U. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Measuring the quantum state of light. , (1997).</li><li>Hong, C. K., Mandel, L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Experimental+realization+of+a+localized+one-photon+state.">Experimental realization of a localized one-photon state.</a> Phys. Rev. Lett. 56, 58-60 (1986).</li><li>Lvovsky, A. I., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Quantum+state+reconstruction+of+the+single-photon+Fock+state.">Quantum state reconstruction of the single-photon Fock state.</a> Phys. Rev. Lett. 87, (2001).</li><li>Ourjoumtsev, A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Generating+optical+Schr&#246;dinger+kittens+for+quantum+information+processing.">Generating optical Schr&#246;dinger kittens for quantum information processing.</a> Science. 312, 83-86 (2006).</li><li>D'Auria, V., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Effect+of+the+heralding+detector+properties+on+the+conditional+generation+of+single-photon+states.">Effect of the heralding detector properties on the conditional generation of single-photon states.</a> Eur. Phys. Journ. D. 66, 249 (2012).</li><li>D'Auria, V., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Quantum+decoherence+of+single-photon+counters.">Quantum decoherence of single-photon counters.</a> Phys. Rev. Lett. 107, (2011).</li><li>Huisman, S. R., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Instant+single-photon+Fock+state+tomography.">Instant single-photon Fock state tomography.</a> Opt. Lett. 34, 2739-2741 (2009).</li><li>Morin, O., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=High-fidelity+single-photon+source+based+on+a+Type+II+optical+parametric+oscillator.">High-fidelity single-photon source based on a Type II optical parametric oscillator.</a> Opt. Lett. 37, 3738-3740 (2012).</li><li>Ou, Z. Y., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Realization+of+the+Einstein-Podolski-Rosen+paradox+for+continuous+variables.">Realization of the Einstein-Podolski-Rosen paradox for continuous variables.</a> Phys. Rev. Lett. 68, 3663-3666 (1992).</li><li>Laurat, J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Type-II Optical Parametric Oscillator: a versatile source of quantum correlations and entanglement in Quantum information with continuous-variables of atoms and light. , (2005).</li><li>Laurat, J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Compact+source+of+Einstein-Podolski-Rosen+entanglement+and+squeezing+at+very+low+noise+frequencies.">Compact source of Einstein-Podolski-Rosen entanglement and squeezing at very low noise frequencies.</a> Phys. Rev. A. 70, (2004).</li><li>D'Auria, V., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Full+characterization+of+Gaussian+bipartite+entangled+states+by+a+single+homodyne+detector.">Full characterization of Gaussian bipartite entangled states by a single homodyne detector.</a> Phys. Rev. Lett. 102, (2009).</li><li>Dakna, M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Generating+Schr&#246;dinger-cat-like+states+by+means+of+conditional+measurements+on+a+beam+splitter.">Generating Schr&#246;dinger-cat-like states by means of conditional measurements on a beam splitter.</a> Phys. Rev. A. 55, 3184-3194 (1997).</li><li>Gerrits, T., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Generation+of+optical+coherent-state+superpositions+by+number-resolved+photon+subtraction+from+the+squeezed+vacuum.">Generation of optical coherent-state superpositions by number-resolved photon subtraction from the squeezed vacuum.</a> Phys. Rev. A. 82, (2010).</li><li>Neergaard-Nielsen, J. S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Generation+of+a+Superposition+of+Odd+Photon+Number+States+for+Quantum+Information+Networks.">Generation of a Superposition of Odd Photon Number States for Quantum Information Networks.</a> Phys. Rev. Lett. 97, (2006).</li><li>Wakui, K., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Photon+subtracted+squeezed+states+generated+with+periodically+poled+KTiOPO4.">Photon subtracted squeezed states generated with periodically poled KTiOPO4.</a> Opt. Express. 15, 3568-3574 (2007).</li><li>Kumar, R., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Versatile+wideband+balanced+detector+for+quantum+optical+homodyne+tomography.">Versatile wideband balanced detector for quantum optical homodyne tomography.</a> Optics Com. 285, 5259-5267 (2012).</li><li>Nielsen, A. E. B., M&#248;lmer, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Single-photon-state+generation+from+a+continuous-wave+nondegenerate+optical+parametric+oscillator.">Single-photon-state generation from a continuous-wave nondegenerate optical parametric oscillator.</a> Phys. Rev. A. 75, (2007).</li><li>Morin, O., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Experimentally+accessing+the+optimal+temporal+mode+of+traveling+quantum+light+states.">Experimentally accessing the optimal temporal mode of traveling quantum light states.</a> Phys. Rev. Lett. 111, 213-602 (2013).</li><li>Lvovsky, A. I., Raymer, M. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Continuous-variable+optical+quantum-state+tomography.">Continuous-variable optical quantum-state tomography.</a> Rev. Mod. Phys. 81, 299-332 (2009).</li><li>Marek, P., Fiurasek, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Elementary+gates+for+quantum+information+with+superposed+coherent+states.">Elementary gates for quantum information with superposed coherent states.</a> Phys. Rev. A. 82, (2010).</li><li>Morin, O., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Remote+creation+of+hybrid+entanglement+between+particle-like+and+wave-like+optical+qubits.">Remote creation of hybrid entanglement between particle-like and wave-like optical qubits.</a> Nat. Photonics. Eprint. , (2013).</li></ol>

The authors declare that they have no competing financial interests.

The conditional preparation technique presented here is always an interplay between the initial bipartite resource and the measurement performed by the heralding detector. These two components strongly influence the quantum properties of the generated state.
First, the purity of the prepared states strongly depends on the one of the initial resource, thus a &#8216;good&#8217; OPO is required. What is a &#8216;good&#8217; OPO? It is a device for which the escape efficiency &#951; is close to un...

The ability to engineer the quantum state of traveling optical fields is a central&#160;requirement for quantum information science and technology1, including quantum communication, computing and metrology. Here, we discuss the preparation and characterization of some specific quantum states using as a primary resource the light emitted by continuous-wave optical parametric oscillators3,4 operated below threshold. Specifically, two systems will be considered &#8211; a type-II phase-matched OPO and a type-I&#160;OPO &#8211; enabling respectively the reliable generation of heralded single-photons and of optical coherent state superpositions (CSS), i.e. states of the form |&#945;&#62; - |-&#945;&#62;. These states are important resources for the implementation of a variety of quantum information protocols, ranging from linear optical quantum computation6 to optical hybrid protocols5,7. Significantly, the method presented here permits obtaining a low admixture of vacuum and the emission into a well-controlled spatiotemporal mode.
Generally speaking, quantum states can be classified as Gaussian states and non-Gaussian states according to the shape of the quasi-probability distribution in phase space called the Wigner function W(x, p)8. For non-Gaussian states, the Wigner function can take negative values, a strong signature of non-classicality. Single-photon or coherent state superpositions are indeed non-Gaussian states.
An efficient procedure for generating such states is known as the conditional preparation technique, where an initial Gaussian resource is combined with a so-called non-Gaussian measurement such as photon counting9,10,11,12,13. This general scheme, probabilistic but heralded, is sketched on Figure 1a.
<img alt="Figure 1" fo:content-width="5in" fo:src="/files/ftp_upload/51224/51224fig1highres.jpg" src="/files/ftp_upload/51224/51224fig1.jpg" /> 
Figure 1.&#160;(a) Conceptual scheme of the conditional preparation technique. (b) Conditional preparation of single-photon state from orthogonally-polarized photon pairs (type-II OPO) separated on a polarizing beam splitter. (c) Conditional preparation of a coherent state superposition by subtracting a single-photon from a squeezed vacuum state (type-I OPO).
By measuring one mode of a bipartite entangled state, the other mode is projected into a state that will depend on this measurement and on the initial entangled resource12,13.
What are the required resource and heralding detector needed to generate the aforementioned states? Single-photon states can be generated using twin beams, i.e. photon-number correlated beams. The detection of a single-photon on one mode then heralds the generation of a single-photon on the other mode9,10,14,15. A frequency-degenerate type-II OPO16,17,18,19 is indeed a well-suited source for this purpose. Signal and idler photons are photon-number correlated and emitted with orthogonal polarizations. Detecting a single-photon on one polarization mode projects the other one into a single-photon state, as shown in Figure 1b.
Concerning coherent state superpositions, they can be generated by subtracting a single-photon from a squeezed vacuum state20 obtained either by pulsed single-pass parametric down-conversion11,21 or by a type-I OPO22,23. The subtraction is performed by tapping a small fraction of the light on a beam-splitter and detecting a single-photon in this mode (Figure 1c). A squeezed vacuum is a superposition of even photon-number states, thus subtracting a single-photon leads to a superposition of odd photon-number states, which has a high fidelity with a linear superposition of two coherent states of equal and small amplitude. For this reason, the name &#8216;Schr&#246;dinger kitten&#8217; has sometimes been given to this state.
The general procedure for generating these states is thus similar, but differs by the primary light source. Filtering of the heralding path and detection techniques are the same whatever the type of OPO used. The present series of protocols detail how to generate these two non-Gaussian states from continuous-wave optical parametric oscillators and how to characterize them with high efficiency.

<table border="0" cellpadding="0" cellspacing="0" width="623">
	<colgroup>
		<col />
		<col />
		<col />
		<col />
	</colgroup>
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Pump laser</td>
			<td style="width:71px;">Innolight</td>
			<td style="width:119px;">Diabolo</td>
			<td style="width:217px;">Dual output, IR and 532 nm</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">KTP and PPKTP crystal</td>
			<td style="width:71px;">Raicol</td>
			<td style="width:119px;"></td>
			<td>Available from other vendors</td>
		</tr>
		<tr height="63">
			<td height="63" style="height:63px;width:216px;">Interferential filters</td>
			<td style="width:71px;">Barr associates</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">High efficiency photodiodes</td>
			<td style="width:71px;">Fermionics</td>
			<td style="width:119px;"></td>
			<td>Quantum efficiency above 97%</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Oscilloscope&#160;</td>
			<td style="width:71px;">Lecroy</td>
			<td style="width:119px;">Wave runner 610 Zi</td>
			<td>Used for data acquisition</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Spectrum analyser</td>
			<td style="width:71px;">Agilent</td>
			<td style="width:119px;">N9000A</td>
			<td>Available from other vendors</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Faraday rotator</td>
			<td style="width:71px;">Qioptic</td>
			<td style="width:119px;">FR-1060-5SC</td>
			<td>Available from other vendors</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">PZT</td>
			<td style="width:71px;">PI</td>
			<td style="width:119px;">P-016.00H</td>
			<td>Available from other vendors</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Superconducting single-photon detectors</td>
			<td style="width:71px;">Scontel</td>
			<td style="width:119px;">SSPD</td>
			<td>low dark counts</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Optical switch</td>
			<td style="width:71px;">Thorlabs</td>
			<td style="width:119px;">OSW12-980E</td>
			<td>Available from other vendors</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;"></td>
			<td style="width:71px;"></td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
	</tbody>
</table>

quantum state engineering of light with continuous-wave optical parametric oscillators

Engineering non-classical states of the electromagnetic field is a central quest for quantum optics1,2. Beyond their fundamental significance, such states are indeed the resources for implementing various protocols, ranging from enhanced metrology to quantum communication and computing. A variety of devices can be used to generate non-classical states, such as single emitters, light-matter interfaces or non-linear systems3. We focus here on the use of a continuous-wave optical parametric oscillator3,4. This system is based on a non-linear &#967;2 crystal inserted inside an optical cavity and it is now well-known as a very efficient source of non-classical light, such as single-mode or two-mode squeezed vacuum depending on the crystal phase matching. 
Squeezed vacuum is a Gaussian state as its quadrature distributions follow a Gaussian statistics. However, it has been shown that number of protocols require non-Gaussian states5. Generating directly such states is a difficult task and would require strong &#967;3 non-linearities. Another procedure, probabilistic but heralded, consists in using a measurement-induced non-linearity via a conditional preparation technique operated on Gaussian states. Here, we detail this generation protocol for two non-Gaussian states, the single-photon state and a superposition of coherent states, using two differently phase-matched parametric oscillators as primary resources. This technique enables achievement of a high fidelity with the targeted state and generation of the state in a well-controlled spatiotemporal mode.

For the type-II OPO and the generation of high-fidelity single photon state: 
The tomographic reconstruction of the heralded state is shown in Figure 2, where the diagonal elements of the reconstructed density matrix and the corresponding Wigner function are displayed. Without any loss corrections, the heralded state exhibits a single-photon component as high as 78%. By taking into account the overall detection losses (15%), the state reaches a fidelity of 91% with a single-photon state. The two-pho...

Watch this Scientific Journal Video about Quantum State Engineering of Light with Continuous-wave Optical Parametric Oscillators at JoVE.com

Quantum State Engineering of Light with Continuous-wave Optical Parametric Oscillators

We describe the reliable generation of non-Gaussian states of traveling optical fields, including single-photon states and coherent state superpositions, using a conditional preparation method operated on the non-classical light emitted by optical parametric oscillators. Type-I and type-II phase-matched oscillators are considered and common procedures, such as the required frequency filtering or the high-efficiency quantum state characterization by homodyning, are detailed.

Engineering non-classical states of the electromagnetic field is a central quest for quantum optics1,2. Beyond their fundamental significance, such states ...

quantum-state-engineering-light-with-continuous-wave-optical

Universidad de Cartagena UDEC

Research

Education

JoVE Core

JoVE Journal

Electrical Engineering

Engineering

Unit 1

Transient and Steady-state Response Analysis

SCIENTISTS IN ACTION

14.4K Views.  Université Pierre et Marie Curie, Ecole Normale Supérieure, CNRS. We describe the reliable generation of non-Gaussian states of traveling optical fields, including single-photon states and coherent state superpositions, using a conditional preparation method operated on the non-classical light emitted by optical parametric oscillators. Type-I and type-II phase-matched oscillators are considered and common procedures, such as the required frequency filtering or the high-efficiency quantum state characterization by homodyning, are detaile...

Video: Quantum State Engineering of Light with Continuous-wave Optical Parametric Oscillators

Quasi-light Storage for Optical Data Packets

Today's telecommunication is based on optical packets which transmit the information in optical fiber networks around the world. Currently, the processing of the signals is done in the electrical domain. Direct storage in the optical domain would avoid the transfer of the packets to the electrical and back to the optical domain in every network node and, therefore, increase the speed and possibly reduce the energy consumption of telecommunications. However, light consists of photons which propagate with the speed of light in vacuum. Thus, the storage of light is a big challenge. There exist some methods to slow down the speed of the light, or to store it in excitations of a medium. However, these methods cannot be used for the storage of optical data packets used in telecommunications networks. Here we show how the time-frequency-coherence, which holds for every signal and therefore for optical packets as well, can be exploited to build an optical memory. We will review the background and show in detail and through examples, how a frequency comb can be used for the copying of an optical packet which enters the memory. One of these time domain copies is then extracted from the memory by a time domain switch. We will show this method for intensity as well as for phase modulated signals.

The article describes a procedure to store optical data packets with an arbitrary modulation, wavelength, and data rate. These packets are the basis of modern telecommunications.

Today's telecommunication is based on optical packets which transmit the information in optical fiber networks around the world. Currently, the processing ...

Gradient Echo Quantum Memory in Warm Atomic Vapor

Gradient echo memory (GEM) is a protocol for storing optical quantum states of light in atomic ensembles. The primary motivation for such a technology is that quantum key distribution (QKD), which uses Heisenberg uncertainty to guarantee security of cryptographic keys, is limited in transmission distance. The development of a quantum repeater is a possible path to extend QKD range, but a repeater will need a quantum memory. In our experiments we use a gas of rubidium 87 vapor that is contained in a warm gas cell. This makes the scheme particularly simple. It is also a highly versatile scheme that enables in-memory refinement of the stored state, such as frequency shifting and bandwidth manipulation. The basis of the GEM protocol is to absorb the light into an ensemble of atoms that has been prepared in a magnetic field gradient. The reversal of this gradient leads to rephasing of the atomic polarization and thus recall of the stored optical state. We will outline how we prepare the atoms and this gradient and also describe some of the pitfalls that need to be avoided, in particular four-wave mixing, which can give rise to optical gain.

The gradient echo memory is a protocol for storing optical quantum states of light in atomic ensembles. Quantum memory is a key element of a quantum repeater, which can extend the range of quantum key distribution. We outline the operation of the scheme when implemented in a 3-level atomic ensemble.

Gradient  echo memory (GEM) is a protocol for storing optical quantum states of light in  atomic ensembles. The primary motivation for such a technology ...

Fabrication and Characterization of Disordered Polymer Optical Fibers for Transverse Anderson Localization of Light

We develop and characterize a disordered polymer optical fiber that uses transverse Anderson localization as a novel waveguiding mechanism. The developed polymer optical fiber is composed of 80,000 strands of poly (methyl methacrylate) (PMMA) and polystyrene (PS) that are randomly mixed and drawn into a square cross section optical fiber with a side width of 250 &mu;m. Initially, each strand is 200 &mu;m in diameter and 8-inches long. During the mixing process of the original fiber strands, the fibers cross over each other; however, a large draw ratio guarantees that the refractive index profile is invariant along the length of the fiber for several tens of centimeters. The large refractive index difference of 0.1 between the disordered sites results in a small localized beam radius that is comparable to the beam radius of conventional optical fibers. The input light is launched from a standard single mode optical fiber using the butt-coupling method and the near-field output beam from the disordered fiber is imaged using a 40X objective and a CCD camera. The output beam diameter agrees well with the expected results from the numerical simulations. The disordered optical fiber presented in this work is the first device-level implementation of 2D Anderson localization, and can potentially be used for image transport and short-haul optical communication systems.

We develop and characterize a disordered polymer optical fiber that uses transverse Anderson localization as a novel waveguiding mechanism. This microstructured fiber can transport a small localized beam with a radius that is comparable to the beam radius of conventional optical fibers.

We develop and characterize a disordered polymer optical fiber that uses transverse Anderson localization as a novel waveguiding mechanism. The developed ...

Fabrication of Uniform Nanoscale Cavities via Silicon Direct Wafer Bonding

Measurements of the heat capacity and superfluid fraction of confined 4He have been performed near the lambda transition using lithographically patterned and bonded silicon wafers. Unlike confinements in porous materials often used for these types of experiments3, bonded wafers provide predesigned uniform spaces for confinement. The geometry of each cell is well known, which removes a large source of ambiguity in the interpretation of data.
Exceptionally flat, 5 cm diameter, 375 &#181;m thick Si wafers with about 1 &#181;m variation over the entire wafer can be obtained commercially (from Semiconductor Processing Company, for example). Thermal oxide is grown on the wafers to define the confinement dimension in the z-direction. A pattern is then etched in the oxide using lithographic techniques so as to create a desired enclosure upon bonding. A hole is drilled in one of the wafers (the top) to allow for the introduction of the liquid to be measured. The wafers are cleaned2 in RCA solutions and then put in a microclean chamber where they are rinsed with deionized water4. The wafers are bonded at RT and then annealed at ~1,100 &#176;C. This forms a strong and permanent bond. This process can be used to make uniform enclosures for measuring thermal and hydrodynamic properties of confined liquids from the nanometer to the micrometer scale.

A method for permanently bonding two silicon wafers so as to realize a uniform enclosure is described. This includes wafer preparation, cleaning, RT bonding, and annealing processes. The resulting bonded wafers (cells) have uniformity of enclosure ~1%1,2. The resulting geometry allows for measurements of confined liquids and gasses.

Measurements of the heat capacity and superfluid fraction of confined 4He have been performed near the lambda transition using lithographically patterned ...

Construction and Characterization of External Cavity Diode Lasers for Atomic Physics

Since their development in the late 1980s, cheap, reliable external cavity diode lasers (ECDLs) have replaced complex and expensive traditional dye and Titanium Sapphire lasers as the workhorse laser of atomic physics labs1,2. Their versatility and prolific use throughout atomic physics in applications such as absorption spectroscopy and laser cooling1,2 makes it imperative for incoming students to gain a firm practical understanding of these lasers. This publication builds upon the seminal work by Wieman3, updating components, and providing a video tutorial. The setup, frequency locking and performance characterization of an ECDL will be described. Discussion of component selection and proper mounting of both diodes and gratings, the factors affecting mode selection within the cavity, proper alignment for optimal external feedback, optics setup for coarse and fine frequency sensitive measurements, a brief overview of laser locking techniques, and laser linewidth measurements are included.

This is an instructional paper to guide the construction and diagnostics of external cavity diode lasers (ECDLs), including component selection and optical alignment, as well as the basics of frequency reference spectroscopy and laser linewidth measurements for applications in the field of atomic physics.

Since their development in the late 1980s, cheap, reliable external cavity diode lasers (ECDLs) have replaced complex and expensive traditional dye and ...

Fabrication and Testing of Microfluidic Optomechanical Oscillators

Cavity optomechanics experiments that parametrically couple the phonon modes and photon modes have been investigated in various optical systems including microresonators. However, because of the increased acoustic radiative losses during direct liquid immersion of optomechanical devices, almost all published optomechanical experiments have been performed in solid phase. This paper discusses a recently introduced hollow microfluidic optomechanical resonator. Detailed methodology is provided to fabricate these ultra-high-Q microfluidic resonators, perform optomechanical testing, and measure radiation pressure-driven breathing mode and SBS-driven whispering gallery mode parametric vibrations. By confining liquids inside the capillary resonator, high mechanical- and optical- quality factors are simultaneously maintained.

Parametric optomechanical excitations have recently been experimentally demonstrated in microfluidic optomechanical resonators by means of optical radiation pressure and stimulated Brillouin scattering. This paper describes the fabrication of these microfluidic resonators along with methodologies for generating and verifying optomechanical oscillations.

Cavity optomechanics experiments that parametrically couple the phonon modes and photon modes have been investigated in various optical systems including ...

Selective Area Modification of Silicon Surface Wettability by Pulsed UV Laser Irradiation in Liquid Environment

The wettability of silicon (Si) is one of the important parameters in the technology of surface functionalization of this material and fabrication of biosensing devices. We report on a protocol of using KrF and ArF lasers irradiating Si (001) samples immersed in a liquid environment with low number of pulses and operating at moderately low pulse fluences to induce Si wettability modification. Wafers immersed for up to 4 hr in a 0.01% H2O2/H2O solution did not show measurable change in their initial contact angle (CA) ~75&#176;. However, the 500-pulse KrF and ArF lasers irradiation of such wafers in a microchamber filled with 0.01% H2O2/H2O solution at 250 and 65 mJ/cm2, respectively, has decreased the CA to near 15&#176;, indicating the formation of a superhydrophilic surface. The formation of OH-terminated Si (001), with no measurable change of the wafer&#8217;s surface morphology, has been confirmed by X-ray photoelectron spectroscopy and atomic force microscopy measurements. The selective area irradiated samples were then immersed in a biotin-conjugated fluorescein-stained nanospheres solution for 2 hr, resulting in a successful immobilization of the nanospheres in the non-irradiated area. This illustrates the potential of&#160;the method for selective area biofunctionalization and fabrication of advanced Si-based biosensing architectures. We also describe a similar protocol of irradiation of wafers immersed in methanol (CH3OH) using ArF laser operating at pulse fluence of 65 mJ/cm2 and in situ formation of a strongly hydrophobic surface of Si (001) with the CA of 103&#176;. The XPS results indicate ArF laser induced formation of Si&#8211;(OCH3)x compounds responsible for the observed hydrophobicity. However, no such compounds were found by XPS on the Si surface irradiated by KrF laser in methanol, demonstrating the inability of the KrF laser to photodissociate methanol and create -OCH3 radicals.

We report on a process of in situ alteration of HF treated Si (001) surface into a hydrophilic or hydrophobic state by irradiating samples in microfluidic chambers filled with&#160;H2O2/H2O solution (0.01%-0.5%) or methanol solutions using pulsed UV laser of a relative low pulse fluence.

The wettability of silicon (Si) is one of the important parameters in the technology of surface functionalization of this material and fabrication of ...

Fabrication of White Light-emitting Electrochemical Cells with Stable Emission from Exciplexes

The authors present an approach for fabricating stable white light emission from polymer light-emitting electrochemical cells (PLECs) having an active layer which consists of blue-fluorescent poly(9,9-di-n-dodecylfluorenyl-2,7-diyl) (PFD) and &#960;-conjugated triphenylamine molecules. This white light emission originates from exciplexes formed between PFD and amines in electronically excited states. A device containing PFD, 4,4&#39;,4&#39;&#39;-tris[2-naphthyl(phenyl)amino]triphenylamine (2-TNATA), Poly(ethylene oxide) and K2CF3SO3 showed white light emission with Commission internationale de l&#39;&#233;clairage (CIE) coordinates of (0.33, 0.43) and a Color Rendering Index (CRI) of Ra = 73 at an applied voltage of 3.5 V. Constant voltage measurements showed that the CIE coordinates of (0.27, 0.37), Ra of 67, and the emission color observed immediately after application of a voltage of 5 V were nearly unchanged and stable after 300 sec.

The authors present a method for fabricating stable white-light-emitting electrochemical cells utilizing emission from exciplexes formed between a blue-emitting fluorene polymer and aromatic amines.

The authors present an approach for fabricating stable white light emission from polymer light-emitting electrochemical cells (PLECs) having an active ...

Scanning Light Scattering Profiler (SLPS) Based Methodology to Quantitatively Evaluate Forward and Backward Light Scattering from Intraocular Lenses

The scanning light scattering profiler (SLSP) methodology has been developed for the full-angle quantitative evaluation of forward and backward light scattering from intraocular lenses (IOLs) using goniophotometer principles. This protocol describes the SLSP platform and how it employs a 360&#176; rotational photodetector sensor that is scanned around an IOL sample while recording the intensity and location of scattered light as it passes through the IOL medium. The SLSP platform can be used to predict, non-clinically, the propensity for current and novel IOL designs and materials to induce light scatter. Non-clinical evaluation of light scattering properties of IOLs can significantly reduce the number of patient complaints related to unwanted glare, glistening, optical defects, poor image quality, and other phenomena associated with the unintended light scattering. Future studies should be conducted to correlate SLSP data with clinical results to help identify which measured light scatter is most problematic for patients that have undergone cataract surgery subsequent to IOL implantation.

Scanning Light Scattering Profiler SLPS Based Methodology to Quantitatively Evaluate Forward and Backward Light Scattering from Intraocular Lenses

This protocol describes the scanning light scattering profiler (SLSP) that enables the full-angle quantitative evaluation of forward and backward scattering of light from intraocular lenses (IOLs) using goniophotometer principles.

The scanning light scattering profiler (SLSP) methodology has been developed for the full-angle quantitative evaluation of forward and backward light ...

High-speed Continuous-wave Stimulated Brillouin Scattering Spectrometer for Material Analysis

Recent years have witnessed a significant increase in the use of spontaneous Brillouin spectrometers for non-contact analysis of soft matter, such as aqueous solutions and biomaterials, with fast acquisition times. Here, we discuss the assembly and operation of a Brillouin spectrometer that uses stimulated Brillouin scattering (SBS) to measure stimulated Brillouin gain (SBG) spectra of water and lipid emulsion-based tissue-like samples in transmission mode with &lt;10 MHz spectral-resolution and &lt;35 MHz Brillouin-shift measurement precision at &lt;100 ms. The spectrometer consists of two nearly counter-propagating continuous-wave (CW) narrow-linewidth lasers at 780 nm whose frequency detuning is scanned through the material Brillouin shift. By using an ultra-narrowband hot rubidium-85 vapor notch filter and a phase-sensitive detector, the signal-to-noise-ratio of the SBG signal is significantly enhanced compared to that obtained with existing CW-SBS spectrometers. This improvement enables measurement of SBG spectra with up to 100-fold faster acquisition times, thereby facilitating high spectral-resolution and high-precision Brillouin analysis of soft materials at high speed.

We describe the construction of a rapid continuous-wave-stimulated-Brillouin-scattering (CW-SBS) spectrometer. The spectrometer employs single-frequency diode-lasers and an atomic vapor notch-filter to acquire transmission spectra of turbid/non-turbid samples with high spectral-resolution at speeds up to 100-fold faster than those of existing CW-SBS spectrometers. This improvement enables high-speed Brillouin material analysis.

Recent years have witnessed a significant increase in the use of spontaneous Brillouin spectrometers for non-contact analysis of soft matter, such as ...