ARTICLE NATURE COMMUNICATIONS DOl:10.1038/comms1263 In as far as the term designates the quantum superposition of two 2.Carnal,O.Mlynek,J.Young's double-slit experiment with atoms:a simple macroscopically distinct states of a highly complex object,the atom interferometer.Phys.Rev.Lett.66,2689-2692(1991). molecules in our new experimental series are among the fattest 3.Zimmermann,B.et al.Localization and loss of coherence in molecular double- slit experiments.Nat.Phys.4,649-655 (2008). Schrodinger cats realized to date.Schrodinger reasoned whether it 4.King,B.,Di Piazza,A.Keitel,C.H.A matterless double slit.Nat.Photonics 4, is possible to bring a cat into a superposition state of being 'dead' 92-94(2010). and 'alive.In our experiment,the superposition consists of having 5.Hasselbach,E.Progress in electron-and ion-interferometry.Rep.Prog.Phys.73, all 430 atoms simultaneously'in the left arm'and 'in the right arm' 016101(2010). of our interferometer,that is,two possibilities that are macroscopi- 6.Rauch,H.Werner,A.Neutron Interferometry:Lessons in Experimental Quantum Mechanics(Oxford University,2000). cally distinct.The path separation is about two orders of magnitude 7.Adams,C.S.,Sigel,M.Mlynek,Atom optics.Phys.Rep.240,143-210 larger than the size of the molecules. (1994). Schrodinger's thought experiment originally also required the Keith,D.W.,Schattenburg,M.L.,Smith,H.I.Pritchard,D.E entanglement between a microscopic atom and the final state of Diffraction of atoms by a transmission grating.Phys.Rev.Lett.61,1580-1583 the macroscopic cat.Such a mechanism is not needed to create (1988). 9. Cronin,A.D.,Schmiedmayer,J.Pritchard,D.E.Optics and the molecular superposition state in our experiment.Entangle- interferometry with atoms and molecules.Rev.Mod.Phys.81, ment between a molecule and a microscopic probe particle does, 1051-1129(2009). however,occur in decoherence processes in which the quantum 10.Arndt,M.et al.Wave-particle duality of C molecules.Nature 401,680-682 interaction with the environment reveals which-path informa- (1999). tion'45 and destroys the interference pattern.Collisions with 11.Hackermuller,L.et al.Wave nature of biomolecules and fluorofullerenes.Phys. Rev.Lett..91,090408(2003). residual gas molecules",the emission of heat radiation3 and the 12.Bruhl,R et al.Diffraction of neutral helium clusters:evidence for 'magic absorption of blackbody radiation are among the most impor- numbers.Phys.Rev.Lett.92,185301 (2004). tant decoherence mechanisms for interferometry with massive 13.Ladd,T.D..Jelezko,E,Laflamme,R.,Nakamura,Y.Monroe,C.&O'Brien,I.L. particles.We estimate that they lead to a visibility reduction of Quantum computers.Nature 464,45-53 (2010). less than 1%under the conditions of the present experimental 14.Zurek,W.H.Decoherence,einselection,and the quantum origins of the classical.Rev.Mod.Phys.75,715-775(2003). arrangement,in spite of the high internal molecular tempera- 15.Joos,E.et al.Decoherence and the Appearance of the Classical World in tures and substantial dipole fluctuations. Quantum Theory (Springer,1996). Specifically for PFNS8,a microscopically realistic account of 16.Ohmori,K.Wave-packet and coherent control dynamics.Annu.Rev.Phys. the decoherence processes2 predicts a visibility reduction of 10% Chem.60.487-511(2009). 17.Fagan,P.et al Production of perfluoroalkylated nanospheres from only if the temperature of either the molecule or the radiation field buckminsterfullerene.Science 262,404-407(1993). exceeds 1,500K,or if the residual nitrogen gas pressure exceeds 18.Deachapunya,S.et al.Slow beams of massive molecules.Eur.Phys.I.D.46, 2×10-7mbar. 307-3132008. In conclusion,our experiments reveal the quantum wave nature 19.Kroto,H.W.,Heath,J.R.,O'Brian,S.C..Curl,R.F.&Smalley,R.E.C60 of tailor-made organic molecules in an unprecedented mass and size Buckminsterfullerene.Nature 318,162-163(1985). 20.Clauser,J.F.in Experimental Metaphysics (eds Cohen,R.S..Home,M. domain.They open a new window for quantum experiments with Stachel,J.)1-11 (Kluwer Academic,1997). nanoparticles in a complexity class comparable to that of small pro- 21.Brezger,B..Arndt,M.&Zeilinger,A.Concepts for near-field interferometers teins,and they demonstrate that it is feasible to create and maintain with large molecules./Opt.B 5,S82-S89 (2003). high quantum coherence with initially thermal systems consisting 22.Gerlich,S.et al.A Kapitza-Dirac-Talbot-Lau interferometer for highly of more than 1,000 internal degrees of freedom. polarizable molecules.Nature Physics 3,711-715 (2007). 23.Hornberger,K.et al.Theory and experimental verification of Kapitza-Dirac- Talbot-Lau interferometry.New J.Phys.11,043032(2009). Methods 24.Frisch,M.J.et al.Gaussian 09,Revision A.1.(Gaussian,Inc.,Wallingford CT. Chemical synthesis.The porphyrin derivatives were synthesized by the attach- 2009). ment of a highly fluorous thiol to meso-tetra(pentafluorophenyl)porphyrin in 25.Tuxen,J.,Gerlich,S.,Eibenberger,S.,Arndt,M.Mayor,M.Quantum a nucleophilic aromatic substitution reaction by applying a modified literature interference distinguishes between constitutional isomers.Chem.Comm.46, procedure.To assemble TPPF84,the commercially available 1H,1H.2H2H- 4145-4147(2010). perfluorododecane-1-thiol as nucleophilic fluorous part was introduced to the 26.Bradley.C.C.,Sackett,C.A.,Tollett,J.J.Hulet,R.G.Evidence of Bose- porphyrin unit.The branched thiol building block for TPPF152 was synthesized Einstein condensation in an atomic gas with attractive interactions.Phys.Rev in three reaction steps.A reaction sequence including mono-functionalization Lett.79,1170(1997). of tris(bromomethyl)benzene with a protected thiol,introduction of two 27.Schrodinger,E.Die gegenwartige Situation in der Quantenmechanik fluorous ponytails and a final deprotection of the thiol functionality yielded the Naturwissenschaften 23,844-849 (1935). desired fluorous thiol suitable for the envisaged substitution reaction.All 28.Brune,M.et al.Observing the progressive decoherence of the 'meter'in a target structures were purified by column chromatography and characterized quantum measurement.Phys.Rev:Lett.77,4887-4890(1996) by nuclear magnetic resonance spectroscopy and mass spectrometry 29.Leibfried,D.et al.Creation of a six-atom 'Schrodinger Cat'state.Nature 438, (Supplementory Methods). 639-642(2005). 30.Monz,T.et al.Coherence of large-scale entanglement.arXiv:1009.6126v Differences between the classical and quantum predictions.The func- [quant-ph](2010). tional dependence of the interference fringe visibility on the laser power 31.Hornberger,K.et al.Collisional decoherence observed in matter wave is qualitatively similar in both a classical and a full quantum treatment.As interferometry.Phys.Rev.Lett.90,160401(2003). observed from the treatment described in ref.23 the abscissa scaling dif- 32.Hackermuller,L.et al.Decoherence of matter waves by thermal emission of fers,however,by the factor E/sin()with=L/where L is the distance radiation.Nature 427,711-714 (2004). between two consecutive gratings and Lr=d/Aas is the Talbot length.For 33.Samaroo,D.,Vinodu,M.,Chen,X.Drain,C.M.Meso-tetra(pentafluorophenyl)- the case of Figure 4,we find /sin()=5.9.The experimental data are in porphyrin as an efficient platform for combinatorial synthesis and the selection clear agreement with the quantum model. of new photodynamic therapeutics using a cancer cell line.I.Comb.Chem.9, 998-1011(2007). Equipment.The diffracting laser beam is generated by a Coherent Verdi V18 laser at 532 nm.The QMS is an Extrel CMS with a rod diameter of 9.5 mm,operated at a radio frequency of 440kHz.The SiN,gratings in G,and G,were made by Dr Tim Acknowledgments Savas,nm2 LLC MIT Cambridge. We thank Lucia Hackermuller(now University of Nottingham)for important contributions to the setup of a first version of this experiment until the end of 2006, and Hendrik Ulbricht(now University of Southampton)for his collaboration until References 2008.We thank Anton Zeilinger for his role as an initiator of the 'foundations of 1.Zeilinger,A.,Gahler,R.,Shull,C.G.,Treimer,W.Mampe,W.Single-and quantum physics'research programme in Vienna.The interference experiments were double-slit diffraction of neutrons.Rev.Mod.Phys.60,1067-1073(1988). financed through the Austrian FWF Wittgenstein grant(Z149-N16),the doctoral NATURE COMMUNICATIONS|2:263 DOl:10.1038/ncomms1263 www.nature.com/naturecommunications 2011 Macmillan Publishers Limited.All rights reserved.ARTICLE  nature communications | DOI: 10.1038/ncomms1263 nature communications | 2:263 | DOI: 10.1038/ncomms1263 | www.nature.com/naturecommunications © 2011 Macmillan Publishers Limited. All rights reserved. In as far as the term designates the quantum superposition of two macroscopically distinct states of a highly complex object, the molecules in our new experimental series are among the fattest Schrödinger cats realized to date. Schrödinger reasoned whether it is possible to bring a cat into a superposition state of being ‘dead’ and ‘alive’. In our experiment, the superposition consists of having all 430 atoms simultaneously ‘in the left arm’ and ‘in the right arm’ of our interferometer, that is, two possibilities that are macroscopi￾cally distinct. The path separation is about two orders of magnitude larger than the size of the molecules. Schrödinger’s thought experiment originally also required the entanglement between a microscopic atom and the final state of the macroscopic cat. Such a mechanism is not needed to create the molecular superposition state in our experiment. Entangle￾ment between a molecule and a microscopic probe particle does, however, occur in decoherence processes in which the quantum interaction with the environment reveals which-path informa￾tion14,15 and destroys the interference pattern. Collisions with residual gas molecules31 , the emission of heat radiation32 and the absorption of blackbody radiation are among the most impor￾tant decoherence mechanisms for interferometry with massive particles. We estimate that they lead to a visibility reduction of less than 1% under the conditions of the present experimental arrangement, in spite of the high internal molecular tempera￾tures and substantial dipole fluctuations. Specifically for PFNS8, a microscopically realistic account of the decoherence processes31,32 predicts a visibility reduction of 10% only if the temperature of either the molecule or the radiation field exceeds 1,500K, or if the residual nitrogen gas pressure exceeds 2×10−7mbar. In conclusion, our experiments reveal the quantum wave nature of tailor-made organic molecules in an unprecedented mass and size domain. They open a new window for quantum experiments with nanoparticles in a complexity class comparable to that of small pro￾teins, and they demonstrate that it is feasible to create and maintain high quantum coherence with initially thermal systems consisting of more than 1,000 internal degrees of freedom. Methods Chemical synthesis. The porphyrin derivatives were synthesized by the attach￾ment of a highly fluorous thiol to meso-tetra(pentafluorophenyl)porphyrin in a nucleophilic aromatic substitution reaction by applying a modified literature procedure33 . To assemble TPPF84, the commercially available 1H,1H,2H,2H￾perfluorododecane-1-thiol as nucleophilic fluorous part was introduced to the porphyrin unit. The branched thiol building block for TPPF152 was synthesized in three reaction steps. A reaction sequence including mono-functionalization of tris(bromomethyl)benzene with a protected thiol, introduction of two fluorous ponytails and a final deprotection of the thiol functionality yielded the desired fluorous thiol suitable for the envisaged substitution reaction. All target structures were purified by column chromatography and characterized by nuclear magnetic resonance spectroscopy and mass spectrometry (Supplementory Methods). Differences between the classical and quantum predictions. The func￾tional dependence of the interference fringe visibility on the laser power is qualitatively similar in both a classical and a full quantum treatment. As observed from the treatment described in ref. 23 the abscissa scaling dif￾fers, however, by the factor ξ/sin(ξ) with ξ = π·L/LT, where L is the distance between two consecutive gratings and LT = d2 /λdB is the Talbot length. For the case of Figure 4, we find ξ/sin(ξ)5.9. The experimental data are in clear agreement with the quantum model. Equipment. The diffracting laser beam is generated by a Coherent Verdi V18 laser at 532nm. The QMS is an Extrel CMS with a rod diameter of 9.5mm, operated at a radio frequency of 440 kHz. The SiNx gratings in G1 and G3 were made by Dr Tim Savas, nm2 LLC & MIT Cambridge. References 1. Zeilinger, A., Gähler, R., Shull, C. G., Treimer, W. & Mampe, W. Single- and double-slit diffraction of neutrons. Rev. Mod. Phys. 60, 1067–1073 (1988). 2. Carnal, O. & Mlynek, J. Young’s double-slit experiment with atoms: a simple atom interferometer. Phys. Rev. Lett. 66, 2689–2692 (1991). 3. Zimmermann, B. et al. Localization and loss of coherence in molecular double￾slit experiments. Nat. Phys. 4, 649–655 (2008). 4. King, B., Di Piazza, A. & Keitel, C. H. A matterless double slit. Nat. Photonics 4, 92–94 (2010). 5. Hasselbach, F. Progress in electron- and ion-interferometry. Rep. Prog. Phys. 73, 016101 (2010). 6. Rauch, H. & Werner, A. 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A Kapitza-Dirac-Talbot-Lau interferometer for highly polarizable molecules. Nature Physics 3, 711–715 (2007). 23. Hornberger, K. et al. Theory and experimental verification of Kapitza-Dirac￾Talbot-Lau interferometry. New J. Phys. 11, 043032 (2009). 24. Frisch, M. J. et al. Gaussian 09, Revision A.1. (Gaussian, Inc., Wallingford CT, 2009). 25. Tüxen, J., Gerlich, S., Eibenberger, S., Arndt, M. & Mayor, M. Quantum interference distinguishes between constitutional isomers. Chem. Comm. 46, 4145–4147 (2010). 26. Bradley, C. C., Sackett, C. A., Tollett, J. J. & Hulet, R. G. Evidence of Bose￾Einstein condensation in an atomic gas with attractive interactions. Phys. Rev. Lett. 79, 1170 (1997). 27. Schrödinger, E. Die gegenwärtige Situation in der Quantenmechanik. Naturwissenschaften 23, 844–849 (1935). 28. Brune, M. et al. Observing the progressive decoherence of the ‘meter’ in a quantum measurement. Phys. Rev. Lett. 77, 4887–4890 (1996). 29. Leibfried, D. et al. Creation of a six-atom ‘Schrödinger Cat’ state. Nature 438, 639–642 (2005). 30. Monz, T. et al. Coherence of large-scale entanglement. arXiv:1009.6126v1 [quant-ph] (2010). 31. Hornberger, K. et al. Collisional decoherence observed in matter wave interferometry. Phys. Rev. Lett. 90, 160401 (2003). 32. Hackermüller, L. et al. Decoherence of matter waves by thermal emission of radiation. Nature 427, 711–714 (2004). 33. Samaroo, D., Vinodu, M., Chen, X. & Drain, C. M. Meso-tetra(pentafluorophenyl)- porphyrin as an efficient platform for combinatorial synthesis and the selection of new photodynamic therapeutics using a cancer cell line. J. Comb. Chem. 9, 998–1011 (2007). Acknowledgments We thank Lucia Hackermüller (now University of Nottingham) for important contributions to the setup of a first version of this experiment until the end of 2006, and Hendrik Ulbricht (now University of Southampton) for his collaboration until 2008. We thank Anton Zeilinger for his role as an initiator of the ‘foundations of quantum physics’ research programme in Vienna. The interference experiments were financed through the Austrian FWF Wittgenstein grant (Z149-N16), the doctoral