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arXiv:1909.07860 · Journal of the Optical Society of America A

Theoretical analysis of quantum random walks with stress-engineered optics

Kevin Liang, Ashan Ariyawansa, Omar S. Magaña‐Loaiza, Thomas G. Brown

Published Dec 18, 2019• 2 citations
arXivHTMLPDF

Abstract

Quantum random walks (QRWs) are random processes in which the resulting probability density of the "walker" state, whose movement is governed by a "coin" state, is described in a nonclassical manner. Previously, Q-plates have been used to demonstrate QRWs with polarization and orbital angular momentum playing the roles of coin and walker states, respectively. In this theoretical analysis, we show how stress-engineered optics can be used to develop new platforms for complex QRWs through relatively simple optical elements. Our work opens up new paths to speed up classical-to-quantum transitions in robust photonic networks.

DOI
10.1364/josaa.37.000135

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We investigate a novel quantum random walk (QRW) model, possibly useful in quantum algorithm implementation, that achieves a quadratically faster diffusion rate compared to its classical counterpart. We evaluate its asymptotic behavior expressed in the form of a limit probability distribution of a double horn shape. Questions of robustness and control of that limit distribution are addressed by introducing a quantum optical cavity in which a resonant Jaynes-Cummings type of interaction between the quantum walk coin system realized in the form of a two-level atom and a laser field is taking place. Driving the optical cavity by means of the coin-field interaction time and the initial quantum coin state, we determine two types of modification of the asymptotic behavior of the QRW. In the first one the limit distribution is robustly reproduced up to a scaling, while in the second one the quantum features of the walk, exemplified by enhanced diffusion rate, are washed out and Gaussian asymptotics prevail. Verification of these findings in an experimental setup that involves two quantum optical cavities that implement the driven QRW and its quantum to classical transition is discussed.

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Asymptotics of a quantum random walk driven by an optical cavity

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We investigate a novel quantum random walk (QRW) model, of possible use in quantum algorithm implementation, that achieves a quadratically faster diffusion rate compared to its classical counterpart. We evaluate its asymptotic behaviour expressed in the form of a limit probability distribution of a double-horn shape. Questions of robustness and control of that limit distribution are addressed by introducing a quantum optical cavity in which a resonant Jaynes–Cummings type of interaction between the quantum walk coin system realized in the form of a two-level atom and a laser field is taking place. Driving the optical cavity by means of the coin–field interaction time and the initial quantum coin state, we determine two types of modification of the asymptotic behaviour of the QRW. In the first one the limit distribution is robustly reproduced up to a scaling, while in the second one the quantum features of the walk, exemplified by an enhanced diffusion rate, are washed out and Gaussian asymptotics prevail. Verification of these findings in an experimental set-up that involves two quantum optical cavities that implement the driven QRW and its quantum to classical transition is discussed.

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Experimental engineering of OAM quantum states with photonics quantum walks (Conference Presentation)

Fabio Sciarrino

The preparation of high-dimensional quan- tum states is of great significance in quantum information sci- ence and technology. Compared to qubits, qudit states – de- scribing quantum systems in d-dimensional spaces – enable stronger foundational tests of quantum mechanics [1–3] and better-performing applications in secure quantum communi- cations [4–9], quantum emulation [10, 11], quantum error cor- rection [12–14], fault-tolerant quantum computation [15–19], and quantum machine learning [20–22]. Needless to say, protocols performed on systems living in Hilbert spaces of large dimension require an increasing degree of control, in light of the large number of parameters required to describe states and operations. Nonetheless, the endeav- our of preparing arbitrary qudit states has been successfully achieved in various physical platforms [11, 23–32]. However, most of these works rely on ad hoc strategies, whose specific dependence on the underpinning dynamics makes their trans- lation across different physical platforms very difficult. A very promising way to achieve the desired full inde- pendence of the physical platform, and thus a higher degree of universality, is the use of the rich dynamics offered by Quantum Walks (QWs) [33–35]. QWs, which can be thought of as the quantum counterparts of classical random walks, describe in their discrete version a high-dimensional qudit, named walker, embedded with an internal two-dimensional degree of freedom, conventionally dubbed coin. At every time step, the walker’s state moves coherently to the neighbouring sites in the lattice, conditionally to its coin state [36]. QWs have been successfully implemented [37] in systems as di- verse as trapped atoms [38] and ions [39, 40], photonic cir- cuits [41–50], and optical lattices [51]. Hence, an approach for state engineering based on their dynamics offers hope of being applicable effectively in a variety of different systems, independently of the details of the physical implementation. While the QW dynamics was previously shown to allow the engineering of specific walker’s states [52, 53], in Ref. [54] a scheme was proposed to use discrete-time QWs on a line to prepare arbitrary qudit states. This is achieved by enhanc- ing the degree of control over the walk’s dynamics through the arrangement of suitable step-dependent coin operations, which affect the coin-walker quantum correlations by de facto steering the state of the walker towards the desired final state, and finally projecting in the coin space. This last operation removes the correlations between walker and coin, thus pro- ducing a pure walker state with the desired features. In light of the large parameter space that characterizes the problem at hand, a systematic approach to the identification of the right set of coin operations and final projection is necessary. Such an analysis was presented in Ref. [54], in which a set of an- alytic conditions, together with suitable numerical optimiza- tions, was shown to guarantee the reaching of arbitrary target states with high probability. In this paper, we make use of the scheme of Ref. [54] to give the first demonstration of a state-engineering protocol based on the controlled dynamics generated by QWs. We use the orbital angular momentum (OAM) degree of freedom of single-photon states as a convenient embodiment of the walker [48, 55, 56]. OAM-based experiments offer the pos- sibility to cover Hilbert spaces of large dimensions in light of the favourable (linear) scaling of the number of optical ele- ments with the size of the walk. Moreover, the scheme al- lows for the full control of the coin operation that is key to the implementation of the walk. In order to demonstrate the ver- satility of our scheme, we focus on the interesting classes of cat-like states and spin-coherent states [57, 58]. Those classes play a critical role in the exploration of the boundaries be- tween quantum and classical physics and whose implementa- tion is, in general, still a challenging task. Furthermore, we show experimentally the capability of engineering arbitrary states. The quality of the states synthesized in our endeavours, and the relative simplicity of the experimental protocol that we have put in place, demonstrate the effectiveness of a hybrid platform for quantum state engineering. Such platform holds together a programmable quantum system, the photonic QW in the angular momentum, and classical optimization al- gorithms for finding the best evolution to reach a certain quantum target. [1] T. Ve ́rtesi, S. Pironio, and N. Brunner, Physical Review Letters 104, 060401 (2010). [2] N. Brunner, D. Cavalcanti, S. Pironio, V. Scarani, and S. Wehner, Reviews of Modern Physics 86, 419 (2014). [3] R. Lapkiewicz, P. Li, C. Schaeff, N. K. Langford, S. Ramelow, M. Wies ́niak, and A. Zeilinger, Nature 474, 490 (2011). [4] H. Bechmann-Pasquinucci and A. Peres, Physical Review Let- ters 85, 3313 (2000). [5] M. Fitzi, N. Gisin, and U. Maurer, Physical Review Letters 87, 217901 (2001). [6] N. J. Cerf, M. Bourennane, A. Karlsson, and N. Gisin, Physical Review Letters 88, 127902 (2002). [7] D. Bruß and C. Macchiavello, Physical Review Letters 88, 127901 (2002). [8] A. Acin, N. Gisin, and V. Scarani, (2003), quant-ph/0303009. [9] N. K. Langford, R. B. Dalton, M. D. Harvey, J. L. O’Brien, G. J. Pryde, A. Gilchrist, S. D. Bartlett, and A. G. White, Physical Review Letters 93, 053601 (2004). [10] I. Buluta and F. Nori, Science 326, 108 (2009). [11] M. Neeley, M. Ansmann, R. C. Bialczak, M. Hofheinz, E. Lucero, A. D. O’Connell, D. Sank, H. Wang, J. Wenner, A. N. Cleland, M. R. Geller, and J. M. Martinis, Science 325, 722 (2009). [12] I. L. Chuang, D. W. Leung, and Y. Yamamoto, Physical Review A 56, 1114 (1997). [13] G. Duclos-Cianci and D. Poulin, Physical Review A 87, 062338 (2013). [14] M. H. Michael, M. Silveri, R. T. Brierley, V. V. Albert, J. Salmilehto, L. Jiang, and S. M. Girvin, Physical Review X 6, 031006 (2016). [15] S. D. Bartlett, H. d. Guise, and B. C. Sanders, Physical Review A 65, 052316 (2002). [16] T. C. Ralph, K. J. Resch, and A. Gilchrist, Physical Review A 75, 022313 (2007). [17] B. P. Lanyon, M. Barbieri, M. P. Almeida, T. Jennewein, T. C. Ralph, K. J. Resch, G. J. Pryde, J. L. O’Brien, A. Gilchrist, and A. G. White, Nature Physics 5, 134 (2009). [18] E. T. Campbell, H. Anwar, and D. E. Browne, Physical Review X 2, 041021 (2012). [19] E. T. Campbell, Physical Review Letters 113, 230501 (2014). [20] M. Schuld, I. Sinayskiy, and F. Petruccione, Contemporary Physics 56, 172 (2015). [21] V. Dunjko and H. J. Briegel, arXiv:1709.02779. [22] J. Biamonte, P. Wittek, N. Pancotti, P. Rebentrost, N. Wiebe, and S. Lloyd, Nature 549, 195 (2017). [23] D. Leibfried, D. M. Meekhof, B. E. King, C. Monroe, W. M. Itano, and D. J. Wineland, Physical Review Letters 77, 4281 (1996). [24] M. Hofheinz, H. Wang, M. Ansmann, R. C. Bialczak, E. Lucero, M. Neeley, A. D. O’Connell, D. Sank, J. Wenner, J. M. Martinis, and A. N. Cleland, Nature 459, 546 (2009). [25] B. Anderson, H. Sosa-Martinez, C. Riofr ́ıo, I. H. Deutsch, and P. S. Jessen, Physical Review Letters 114, 240401 (2015). [26] S. P. Walborn, D. S. Lemelle, M. P. Almeida, and P. H. S. Ribeiro, Physical Review Letters 96, 090501 (2006). [27] G. Lima, L. Neves, R. Guzma ́n, E. S. Go ́mez, W. A. T. Nogueira, A. Delgado, A. Vargas, and C. Saavedra, Optics Express 19, 3542 (2011). [28] A. Rossi, G. Vallone, A. Chiuri, F. De Martini, and P. Mataloni, Physical Review Letters 102, 153902 (2009). [29] A. C. Dada, J. Leach, G. S. Buller, M. J. Padgett, and E. Andersson, Nature Physics 7, 677 (2011). [30] R. W. Heeres, P. Reinhold, N. Ofek, L. Frunzio, L. Jiang, M. H. Devoret, and R. J. Schoelkopf, Nature Communications 8, 94 (2017). [31] S. Rosenblum, Y. Y. Gao, P. Reinhold, C. Wang, C. J. Axline, L. Frunzio, S. M. Girvin, L. Jiang, M. Mirrahimi, M. H. Devoret, and R. J. Schoelkopf, Nature Comm. 9, 652 (2018). [32] Y. Chu, P. Kharel, T. Yoon, L. Frunzio, P. T. Rakich, and R. J. Schoelkopf, (2018), arXiv:1804.07426. [33] Y. Aharonov, L. Davidovich, and N. Zagury, Physical Review A 48, 1687 (1993). [34] J. Kempe, Contemporary Physics 44, 307 (2003). [35] S. E. Venegas-Andraca, Quantum Information Processing 11, 1015 (2012). [36] A. Ambainis, E. Bach, A. Nayak, A. Vishwanath, and J. Watrous, in STOC ’01 Proceedings of the thirty-third annual ACM symposium on Theory of computing (2001) pp. 37–49. [37] K. Manouchehri and J. Wang, Physical Implementation of Quantum Walks (Springer Berlin Heidelberg, Berlin, Heidelberg, 2014). [38] R. Coˆte ́, A. Russell, E. E. Eyler, and P. L. Gould, New Journal of Physics 8, 156 (2006). [39] H. Schmitz, R. Matjeschk, C. Schneider, J. Glueckert, M. Enderlein, T. Huber, and T. Schaetz, Physical Review Letters 103, 090504 (2009). [40] F. Za ̈hringer, G. Kirchmair, R. Gerritsma, E. Solano, R. Blatt, and C. F. Roos, Physical Review Letters 104, 100503 (2010). [41] H. B. Perets, Y. Lahini, F. Pozzi, M. Sorel, R. Morandotti, and Y. Silberberg, Physical Review Letters 100, 170506 (2008). [42] A. Peruzzo, M. Lobino, J. C. F. Matthews, N. Matsuda, A. Politi, K. Poulios, X.-Q. Zhou, Y. Lahini, N. Ismail, K. Wo ̈rhoff, Y. Bromberg, Y. Silberberg, M. G. Thompson, and J. L. O’Brien, Science 329, 1500 (2010). [43] M. A. Broome, A. Fedrizzi, B. P. Lanyon, I. Kassal, A. Aspuru- Guzik, and A. G. White, Phys. Rev. Lett. 104, 153602 (2010). [44] A. Schreiber, K. N. Cassemiro, V. Potocˇek, A. Ga ́bris, P. J. Mosley, E. Andersson, I. Jex, and C. Silberhorn, Physical Re- view Letters 104, 050502 (2010). [45] P. P. Rohde, A. Schreiber, M. Sˇtefanˇa ́k, I. Jex, and C. Silber- horn, New Journal of Physics 13, 013001 (2011). [46] L. Sansoni, F. Sciarrino, G. Vallone, P. Mataloni, A. Crespi, R. Ramponi, and R. Osellame, Physical Review Letters 108, 010502 (2012). [47] J. Boutari, A. Feizpour, S. Barz, C. Di Franco, M. S. Kim, W. S. Kolthammer, and I. A. Walmsley, Journal of Optics 18, 094007 (2016). [48] F. Cardano, F. Massa, H. Qassim, E. Karimi, S. Slussarenko, D. Paparo, C. de Lisio, F. Sciarrino, E. Santamato, R. W. Boyd, and L. Marrucci, Science Advances 1, e1500087 (2015). [49] F. Cardano, M. Maffei, F. Massa, B. Piccirillo, C. de Lisio, G. D. Filippis, V. Cataudella, E. Santamato, and L. Marrucci, Nature Communications 7, 11439 (2016). [50] F. Caruso, A. Crespi, A. G. Ciriolo, F. Sciarrino, and R. Osel- lame, Nature Communications 7, 11682 (2016). [51] F. Meinert, M. J. Mark, E. Kirilov, K. Lauber, P. Weinmann, M. Grobner, A. J. Daley, H.-C. Nagerl, N. Ismail, K. Wo ̈rhoff, Y. Bromberg, Y. Silberberg, M. G. Thompson, and J. L. OBrien, Science 344, 1259 (2014). [52] C. M. Chandrashekar, R. Srikanth, and R. Laflamme, Physical Review A 77, 032326 (2008). [53] H. Majury, J. Boutari, E. O’Sullivan, A. Ferraro, and M. Pater- nostro, EPJ Quant. Tech. 5, 1 (2018). [54] L. Innocenti, H. Majury, T. Giordani, N. Spagnolo, F. Sciar- rino, M. Paternostro, and A. Ferraro, Phys. Rev. A 96, 062326 (2017). [55] P.Zhang,B.H.Liu,R.F.Liu,H.R.Li,F.L.Li, andG.C. Guo, Physical Review Letters 81 (2010). [56] S. K. Goyal, F. S. Roux, A. Forbes, and T. Konrad, Physical Review Letters 110, 263602 (2013). [57] M. Brune, S. Haroche, J. M. Raimond, L. Davidovich, and N. Zagury, Phys. Rev. A 45, 5193 (1992). [58] C. Monroe, D. M. Meekhof, B. E. King, and D. J. Wineland, Science 272, 1131 (24 May 1996).

Complex Light and Optical Forces•Mar 8, 2019•0 citations

Coherent random walks in free space

Toni Eichelkraut, Christian Vetter, Armando Pérez-Leija +3 more

Two-dimensional continuous time quantum random walks (CTQRW) are physical processes where quantum particles simultaneously evolve in different permissible directions within discrete graphs. In order to force the quantum walkers (QWs) to evolve in such a fashion, one generally requires periodic potentials. Here, we demonstrate that two-dimensional CTQRW can be generated in free space by properly tailoring the initial wave functions. We analytically show that within a certain spatial region the arising probability distribution quantitatively resembles the probability pattern exhibited by a QW traversing a periodic lattice potential. These theoretical predictions were experimentally verified using classical laser light, appropriately shaped by a spatial light modulator. Expanding the presented results to the case of multiple walkers may open new possibilities in quantum information technology using bulk optics. (C) 2014 Optical Society of America

Optica•Oct 17, 2014•20 citations
Quantum random walks (QRWs) are random processes in which the resulting probability density of the "walker" state, whose movement is governed by a "coin" state, is described in a nonclassical manner. Previously, Q-plates have been used to demonstrate QRWs with polarization and orbital angular momentum playing the roles of coin and walker states, respectively. In this theoretical analysis, we show how stress-engineered optics can be used to develop new platforms for complex QRWs through relatively simple optical elements. Our work opens up new paths to speed up classical-to-quantum transitions in robust photonic networks.
Classical optics can be used to efficiently implement certain quantum information processing tasks with a high degree of control, for example, one-dimensional quantum walks through the space of orbital angular momentum of light directed by its polarization. To explore the potential of quantum information processing with classical light, we here suggest a method to realize ddd-dimensional quantum walks with classical optics---an important step towards robust implementation of certain quantum algorithms. In this scheme, different degrees of freedom of light, such as frequency, orbital angular momentum, and time bins, represent different directions for the walker while the coin to decide which direction the walker takes is realized by employing the polarization combined with different light paths.
We present the first robust implementation of a coined quantum walk over five steps using only passive optical elements. By employing a fiber network loop we keep the amount of required resources constant as the walker's position Hilbert space is increased. We observed a non-Gaussian distribution of the walker's final position, thus characterizing a faster spread of the photon wave packet in comparison to the classical random walk. The walk is realized for many different coin settings and initial states, opening the way for the implementation of a quantum-walk-based search algorithm.
We investigate a novel quantum random walk (QRW) model, possibly useful in quantum algorithm implementation, that achieves a quadratically faster diffusion rate compared to its classical counterpart. We evaluate its asymptotic behavior expressed in the form of a limit probability distribution of a double horn shape. Questions of robustness and control of that limit distribution are addressed by introducing a quantum optical cavity in which a resonant Jaynes-Cummings type of interaction between the quantum walk coin system realized in the form of a two-level atom and a laser field is taking place. Driving the optical cavity by means of the coin-field interaction time and the initial quantum coin state, we determine two types of modification of the asymptotic behavior of the QRW. In the first one the limit distribution is robustly reproduced up to a scaling, while in the second one the quantum features of the walk, exemplified by enhanced diffusion rate, are washed out and Gaussian asymptotics prevail. Verification of these findings in an experimental setup that involves two quantum optical cavities that implement the driven QRW and its quantum to classical transition is discussed.
We investigate a novel quantum random walk (QRW) model, of possible use in quantum algorithm implementation, that achieves a quadratically faster diffusion rate compared to its classical counterpart. We evaluate its asymptotic behaviour expressed in the form of a limit probability distribution of a double-horn shape. Questions of robustness and control of that limit distribution are addressed by introducing a quantum optical cavity in which a resonant Jaynes–Cummings type of interaction between the quantum walk coin system realized in the form of a two-level atom and a laser field is taking place. Driving the optical cavity by means of the coin–field interaction time and the initial quantum coin state, we determine two types of modification of the asymptotic behaviour of the QRW. In the first one the limit distribution is robustly reproduced up to a scaling, while in the second one the quantum features of the walk, exemplified by an enhanced diffusion rate, are washed out and Gaussian asymptotics prevail. Verification of these findings in an experimental set-up that involves two quantum optical cavities that implement the driven QRW and its quantum to classical transition is discussed.
The preparation of high-dimensional quan- tum states is of great significance in quantum information sci- ence and technology. Compared to qubits, qudit states – de- scribing quantum systems in d-dimensional spaces – enable stronger foundational tests of quantum mechanics [1–3] and better-performing applications in secure quantum communi- cations [4–9], quantum emulation [10, 11], quantum error cor- rection [12–14], fault-tolerant quantum computation [15–19], and quantum machine learning [20–22]. Needless to say, protocols performed on systems living in Hilbert spaces of large dimension require an increasing degree of control, in light of the large number of parameters required to describe states and operations. Nonetheless, the endeav- our of preparing arbitrary qudit states has been successfully achieved in various physical platforms [11, 23–32]. However, most of these works rely on ad hoc strategies, whose specific dependence on the underpinning dynamics makes their trans- lation across different physical platforms very difficult. A very promising way to achieve the desired full inde- pendence of the physical platform, and thus a higher degree of universality, is the use of the rich dynamics offered by Quantum Walks (QWs) [33–35]. QWs, which can be thought of as the quantum counterparts of classical random walks, describe in their discrete version a high-dimensional qudit, named walker, embedded with an internal two-dimensional degree of freedom, conventionally dubbed coin. At every time step, the walker’s state moves coherently to the neighbouring sites in the lattice, conditionally to its coin state [36]. QWs have been successfully implemented [37] in systems as di- verse as trapped atoms [38] and ions [39, 40], photonic cir- cuits [41–50], and optical lattices [51]. Hence, an approach for state engineering based on their dynamics offers hope of being applicable effectively in a variety of different systems, independently of the details of the physical implementation. While the QW dynamics was previously shown to allow the engineering of specific walker’s states [52, 53], in Ref. [54] a scheme was proposed to use discrete-time QWs on a line to prepare arbitrary qudit states. This is achieved by enhanc- ing the degree of control over the walk’s dynamics through the arrangement of suitable step-dependent coin operations, which affect the coin-walker quantum correlations by de facto steering the state of the walker towards the desired final state, and finally projecting in the coin space. This last operation removes the correlations between walker and coin, thus pro- ducing a pure walker state with the desired features. In light of the large parameter space that characterizes the problem at hand, a systematic approach to the identification of the right set of coin operations and final projection is necessary. Such an analysis was presented in Ref. [54], in which a set of an- alytic conditions, together with suitable numerical optimiza- tions, was shown to guarantee the reaching of arbitrary target states with high probability. In this paper, we make use of the scheme of Ref. [54] to give the first demonstration of a state-engineering protocol based on the controlled dynamics generated by QWs. We use the orbital angular momentum (OAM) degree of freedom of single-photon states as a convenient embodiment of the walker [48, 55, 56]. OAM-based experiments offer the pos- sibility to cover Hilbert spaces of large dimensions in light of the favourable (linear) scaling of the number of optical ele- ments with the size of the walk. Moreover, the scheme al- lows for the full control of the coin operation that is key to the implementation of the walk. In order to demonstrate the ver- satility of our scheme, we focus on the interesting classes of cat-like states and spin-coherent states [57, 58]. Those classes play a critical role in the exploration of the boundaries be- tween quantum and classical physics and whose implementa- tion is, in general, still a challenging task. Furthermore, we show experimentally the capability of engineering arbitrary states. The quality of the states synthesized in our endeavours, and the relative simplicity of the experimental protocol that we have put in place, demonstrate the effectiveness of a hybrid platform for quantum state engineering. Such platform holds together a programmable quantum system, the photonic QW in the angular momentum, and classical optimization al- gorithms for finding the best evolution to reach a certain quantum target. [1] T. Ve ́rtesi, S. Pironio, and N. Brunner, Physical Review Letters 104, 060401 (2010). [2] N. Brunner, D. Cavalcanti, S. Pironio, V. Scarani, and S. Wehner, Reviews of Modern Physics 86, 419 (2014). [3] R. Lapkiewicz, P. Li, C. Schaeff, N. K. Langford, S. Ramelow, M. Wies ́niak, and A. Zeilinger, Nature 474, 490 (2011). [4] H. Bechmann-Pasquinucci and A. Peres, Physical Review Let- ters 85, 3313 (2000). [5] M. Fitzi, N. Gisin, and U. Maurer, Physical Review Letters 87, 217901 (2001). [6] N. J. Cerf, M. Bourennane, A. Karlsson, and N. Gisin, Physical Review Letters 88, 127902 (2002). [7] D. Bruß and C. Macchiavello, Physical Review Letters 88, 127901 (2002). [8] A. Acin, N. Gisin, and V. Scarani, (2003), quant-ph/0303009. [9] N. K. Langford, R. B. Dalton, M. D. Harvey, J. L. O’Brien, G. J. Pryde, A. Gilchrist, S. D. Bartlett, and A. G. White, Physical Review Letters 93, 053601 (2004). [10] I. Buluta and F. Nori, Science 326, 108 (2009). [11] M. Neeley, M. Ansmann, R. C. Bialczak, M. Hofheinz, E. Lucero, A. D. O’Connell, D. Sank, H. Wang, J. Wenner, A. N. Cleland, M. R. Geller, and J. M. Martinis, Science 325, 722 (2009). [12] I. L. Chuang, D. W. Leung, and Y. Yamamoto, Physical Review A 56, 1114 (1997). [13] G. Duclos-Cianci and D. Poulin, Physical Review A 87, 062338 (2013). [14] M. H. Michael, M. Silveri, R. T. Brierley, V. V. Albert, J. Salmilehto, L. Jiang, and S. M. Girvin, Physical Review X 6, 031006 (2016). [15] S. D. Bartlett, H. d. Guise, and B. C. Sanders, Physical Review A 65, 052316 (2002). [16] T. C. Ralph, K. J. Resch, and A. Gilchrist, Physical Review A 75, 022313 (2007). [17] B. P. Lanyon, M. Barbieri, M. P. Almeida, T. Jennewein, T. C. Ralph, K. J. Resch, G. J. Pryde, J. L. O’Brien, A. Gilchrist, and A. G. White, Nature Physics 5, 134 (2009). [18] E. T. Campbell, H. Anwar, and D. E. Browne, Physical Review X 2, 041021 (2012). [19] E. T. Campbell, Physical Review Letters 113, 230501 (2014). [20] M. Schuld, I. Sinayskiy, and F. Petruccione, Contemporary Physics 56, 172 (2015). [21] V. Dunjko and H. J. Briegel, arXiv:1709.02779. [22] J. Biamonte, P. Wittek, N. Pancotti, P. Rebentrost, N. Wiebe, and S. Lloyd, Nature 549, 195 (2017). [23] D. Leibfried, D. M. Meekhof, B. E. King, C. Monroe, W. M. Itano, and D. J. Wineland, Physical Review Letters 77, 4281 (1996). [24] M. Hofheinz, H. Wang, M. Ansmann, R. C. Bialczak, E. Lucero, M. Neeley, A. D. O’Connell, D. Sank, J. Wenner, J. M. Martinis, and A. N. Cleland, Nature 459, 546 (2009). [25] B. Anderson, H. Sosa-Martinez, C. Riofr ́ıo, I. H. Deutsch, and P. S. Jessen, Physical Review Letters 114, 240401 (2015). [26] S. P. Walborn, D. S. Lemelle, M. P. Almeida, and P. H. S. Ribeiro, Physical Review Letters 96, 090501 (2006). [27] G. Lima, L. Neves, R. Guzma ́n, E. S. Go ́mez, W. A. T. Nogueira, A. Delgado, A. Vargas, and C. Saavedra, Optics Express 19, 3542 (2011). [28] A. Rossi, G. Vallone, A. Chiuri, F. De Martini, and P. Mataloni, Physical Review Letters 102, 153902 (2009). [29] A. C. Dada, J. Leach, G. S. Buller, M. J. Padgett, and E. Andersson, Nature Physics 7, 677 (2011). [30] R. W. Heeres, P. Reinhold, N. Ofek, L. Frunzio, L. Jiang, M. H. Devoret, and R. J. Schoelkopf, Nature Communications 8, 94 (2017). [31] S. Rosenblum, Y. Y. Gao, P. Reinhold, C. Wang, C. J. Axline, L. Frunzio, S. M. Girvin, L. Jiang, M. Mirrahimi, M. H. Devoret, and R. J. Schoelkopf, Nature Comm. 9, 652 (2018). [32] Y. Chu, P. Kharel, T. Yoon, L. Frunzio, P. T. Rakich, and R. J. Schoelkopf, (2018), arXiv:1804.07426. [33] Y. Aharonov, L. Davidovich, and N. Zagury, Physical Review A 48, 1687 (1993). [34] J. Kempe, Contemporary Physics 44, 307 (2003). [35] S. E. Venegas-Andraca, Quantum Information Processing 11, 1015 (2012). [36] A. Ambainis, E. Bach, A. Nayak, A. Vishwanath, and J. Watrous, in STOC ’01 Proceedings of the thirty-third annual ACM symposium on Theory of computing (2001) pp. 37–49. [37] K. Manouchehri and J. Wang, Physical Implementation of Quantum Walks (Springer Berlin Heidelberg, Berlin, Heidelberg, 2014). [38] R. Coˆte ́, A. Russell, E. E. Eyler, and P. L. Gould, New Journal of Physics 8, 156 (2006). [39] H. Schmitz, R. Matjeschk, C. Schneider, J. Glueckert, M. Enderlein, T. Huber, and T. Schaetz, Physical Review Letters 103, 090504 (2009). [40] F. Za ̈hringer, G. Kirchmair, R. Gerritsma, E. Solano, R. Blatt, and C. F. Roos, Physical Review Letters 104, 100503 (2010). [41] H. B. Perets, Y. Lahini, F. Pozzi, M. Sorel, R. Morandotti, and Y. Silberberg, Physical Review Letters 100, 170506 (2008). [42] A. Peruzzo, M. Lobino, J. C. F. Matthews, N. Matsuda, A. Politi, K. Poulios, X.-Q. Zhou, Y. Lahini, N. Ismail, K. Wo ̈rhoff, Y. Bromberg, Y. Silberberg, M. G. Thompson, and J. L. O’Brien, Science 329, 1500 (2010). [43] M. A. Broome, A. Fedrizzi, B. P. Lanyon, I. Kassal, A. Aspuru- Guzik, and A. G. White, Phys. Rev. Lett. 104, 153602 (2010). [44] A. Schreiber, K. N. Cassemiro, V. Potocˇek, A. Ga ́bris, P. J. Mosley, E. Andersson, I. Jex, and C. Silberhorn, Physical Re- view Letters 104, 050502 (2010). [45] P. P. Rohde, A. Schreiber, M. Sˇtefanˇa ́k, I. Jex, and C. Silber- horn, New Journal of Physics 13, 013001 (2011). [46] L. Sansoni, F. Sciarrino, G. Vallone, P. Mataloni, A. Crespi, R. Ramponi, and R. Osellame, Physical Review Letters 108, 010502 (2012). [47] J. Boutari, A. Feizpour, S. Barz, C. Di Franco, M. S. Kim, W. S. Kolthammer, and I. A. Walmsley, Journal of Optics 18, 094007 (2016). [48] F. Cardano, F. Massa, H. Qassim, E. Karimi, S. Slussarenko, D. Paparo, C. de Lisio, F. Sciarrino, E. Santamato, R. W. Boyd, and L. Marrucci, Science Advances 1, e1500087 (2015). [49] F. Cardano, M. Maffei, F. Massa, B. Piccirillo, C. de Lisio, G. D. Filippis, V. Cataudella, E. Santamato, and L. Marrucci, Nature Communications 7, 11439 (2016). [50] F. Caruso, A. Crespi, A. G. Ciriolo, F. Sciarrino, and R. Osel- lame, Nature Communications 7, 11682 (2016). [51] F. Meinert, M. J. Mark, E. Kirilov, K. Lauber, P. Weinmann, M. Grobner, A. J. Daley, H.-C. Nagerl, N. Ismail, K. Wo ̈rhoff, Y. Bromberg, Y. Silberberg, M. G. Thompson, and J. L. OBrien, Science 344, 1259 (2014). [52] C. M. Chandrashekar, R. Srikanth, and R. Laflamme, Physical Review A 77, 032326 (2008). [53] H. Majury, J. Boutari, E. O’Sullivan, A. Ferraro, and M. Pater- nostro, EPJ Quant. Tech. 5, 1 (2018). [54] L. Innocenti, H. Majury, T. Giordani, N. Spagnolo, F. Sciar- rino, M. Paternostro, and A. Ferraro, Phys. Rev. A 96, 062326 (2017). [55] P.Zhang,B.H.Liu,R.F.Liu,H.R.Li,F.L.Li, andG.C. Guo, Physical Review Letters 81 (2010). [56] S. K. Goyal, F. S. Roux, A. Forbes, and T. Konrad, Physical Review Letters 110, 263602 (2013). [57] M. Brune, S. Haroche, J. M. Raimond, L. Davidovich, and N. Zagury, Phys. Rev. A 45, 5193 (1992). [58] C. Monroe, D. M. Meekhof, B. E. King, and D. J. Wineland, Science 272, 1131 (24 May 1996).
Two-dimensional continuous time quantum random walks (CTQRW) are physical processes where quantum particles simultaneously evolve in different permissible directions within discrete graphs. In order to force the quantum walkers (QWs) to evolve in such a fashion, one generally requires periodic potentials. Here, we demonstrate that two-dimensional CTQRW can be generated in free space by properly tailoring the initial wave functions. We analytically show that within a certain spatial region the arising probability distribution quantitatively resembles the probability pattern exhibited by a QW traversing a periodic lattice potential. These theoretical predictions were experimentally verified using classical laser light, appropriately shaped by a spatial light modulator. Expanding the presented results to the case of multiple walkers may open new possibilities in quantum information technology using bulk optics. (C) 2014 Optical Society of America