We present a classical analog of quantum optical deformed oscillators in arrays of waveguides. The normal modes of these one-dimensional photonic crystals are given in terms of Jacobi polynomials. We show that it is possible to attack the problem via factorization by exploiting the corresponding quantum optical model. This allows us to provide an unbroken supersymmetric partner of the proposed Jacobi lattices. Thanks to the underlying SU(1, 1) group symmetry of the lattices, we present the analytic propagators and impulse functions for these one-dimensional photonic crystals.
© 2014 Optical Society of America
Supersymmetry (SUSY) was first used as a way to unify bosonic and fermionic sectors in string models and, along the time, it has been used to unify space-time and internal symmetries in high energy physics, to generalize gravity in relativistic physics, to find and categorize analytically solvable potentials in quantum mechanics, just to mention a few examples [1–3]. In optics, planar waveguides with some particular refractive index profiles have been shown to accept isospectral partners in the paraxial regime  and SUSY has provided a method to generate a family of isospectral potentials to optimize quantum cascade lasers [5, 6]. In quantum optics, isospectral partners for ion-trap Hamiltonians have been used to propose entanglement generation by adiabatic ground-state transition , the simulation of the Wess-Zumino SUSY model in 2+1 dimensions with cold atom-molecule mixtures in the presence of a two-dimensional optical lattice  and that of the electric dipole moment of neutral relativistic particles related to SUSY models in ion-traps setups .
Optical analogies of quantum systems realized in waveguide arrays have recently impacted the field of integrated optical structures . In particular, SUSY photonic lattices can be used to provide phase matching conditions between large number of modes allowing the pairing of isospectral crystals [11, 12]. In the following, we provide a class of photonic lattices showing discrete-SUSY and find their analytic spectrum, propagator and impulse function. Our one-dimensional crystals are also the classical analog to a class of generalized deformed oscillators [13, 14] and can simulate non-classical squeezed light with the propagation of classical light . The normal modes coefficients of these waveguide arrays are given in terms of Jacobi polynomials and this the origin of their denomination. We follow a factorization method  to study our Jacobi lattices and to propose a feasible SUSY parter for them. The analogy between the quantum and the classical optics systems allows us to present a closed form for the propagator and impulse function of our photonic crystals.
2. Jacobi lattices
Let us consider the Schödinger-like equation for a generalized deformed oscillator ,Fig. 1 [17, 18], such that we have a classical analog for our quantum optics system. The experimental realization of this class of photonic lattices is feasible; cf. a discussion on a similar type of refractive index scaling and coupling given in [19–21] and the fact that our lattices are a particular subclass of those given in  with parameters N = 1, βi = 1 + α2 and βs = 0. In order to study our waveguide array, we will take advantage of the quantum optics model and follow an algebraic approach . For this reason, we can rewrite the Schrödinger-like equation in (1) as −i∂z|ψ〉 = Ĥ|ψ〉 with the Hamiltonian, (3) by use of the rotation , 22]. It is for this reason that we christen our waveguide arrays as Jacobi lattices. Figure 2 shows the squared amplitudes of the ground and tenth normal mode for different values of the deformation parameter.
As we have shown in the past for a photonic lattice with SU(2) symmetry , we can follow an equivalent algebraic approach with the SU(1, 1) group and calculate the propagator function by using the quantum optics analogy:(3) is a compact operator we will expect coherent oscillations for a single waveguide input as shown in Fig. 3(a) for an initial classical field impinging at the tenth waveguide, j = 9, of a Jacobi array with parameter α = 0.5; although (3) is composed by compact, K̃0, and non-compact, (K̃+ + K̃−), members of SU(1, 1) the relation 1 + α2 ≥ |α| makes it a compact operator , The numerical and theoretical results are in good agreement, Fig. 3(b), with differences of the order of 10−15. We used a lattice size of 200 waveguides in the numerical simulations, which is in the experimental range, and the light intensity at the last waveguide was of the order of 10−17 for the example shown in Fig. 3.
3. SUSY partner for Jacobi lattices
By defining deformed, nonlinear, parametrized creation and anihilation operators,(1) into 1] to our Jacobi lattice in the form: Fig. 4. Here, we have to use an alternative representation for the elements of the SU(1, 1) group: K̃0 = n̂ + 1/2, and such that the equivalent partner Hamiltonian for the quantum optics analog is given by (7), 22]. Note that the lower energy normal mode is annihilated as expected from the annihilation operator, , and we can classify the SUSY as unbroken . Using the properties of Jacobi polynomials , it possible to show that the rest of the normal modes of the isospectral partner are related to the normal modes of the Jacobi lattice as Figure 5 shows a diagram approach relating the normal modes of both photonic lattices and their spectra.
The propagator for this isospectral partner of our Jacobi lattices is given byFigure 6(a) shows the intensity from a numerical propagation of a beam of light impinging the twentieth, j = 19, waveguide of a Jacobi SUSY partner lattice with deformation parameter α = 0.5. In this simulation the lattice was composed by 200 waveguides and the field intensity at the last waveguide was always smaller than 7 × 10−6. We compare the squared impulse function versus the numerical intensity at the j = 19 waveguide in Fig. 6(b) where we can see the expected coherent oscillation of the field amplitude.
We have taken advantage of factorization techniques in quantum mechanics to propose two classical isospectral photonic lattices such that their quantum optics analogies are defined by the Hamiltonians and its SUSY partner with α ∈ ℝ and α ≠ ±1. These Hamiltonians are related in such a way, and , that their spectra are identical, , and their normal modes are related through the deformed creation (annihilation) operators, for k ≥ 1 and . The two waveguide arrays correspond to an unbroken SUSY because the annihilation operator annihilates the ground state of the partner, . We have named these arrays of waveguides Jacobi lattices because the amplitudes of their normal modes are given in terms of Jacobi polynomials. The arrays are feasible of experimental realization as the individual waveguides require a linearly increasing refractive index while the couplings between waveguides follow a square root distribution in the Jacobi lattice and increase linearly in the SUSY partner. These lattices show a SU(1, 1) symmetry with group parameter k = 1 for the Jacobi lattice and k = 1/2 for its partner that allowed us to present an analytic propagator for them. The analog Hamiltonian operators of our photonic lattices are compact, this guarantees that the impulse functions will show coherent oscillations and we could keep the size of the lattices finite depending on the initial field amplitudes.
HMMC is grateful to P. Aleahmad for fruitful discussions.
References and links
1. F. Cooper, A. Khare, and U. Sukhatme, “Supersymmetry and quantum mechanics,” Phys. Rep. 251, 267–385 (1995). [CrossRef]
2. D. J. Fernández C. and N. Fernández-García, “Higher-order supersymmetric quantum mechanics,” AIP Conf. Proc. 744, 236–273 (2005). [CrossRef]
3. D. J. Fernández C., “Supersymmetric quantum mechanics,” AIP Conf. Proc. 1287, 3–36 (2010).
4. S. M. Chumakov and K. B. Wolf, “Supersymmetry in Helmholtz optics,” Phys. Lett. A 193, 51–53 (1994). [CrossRef]
5. S. Tomić, V. Milanović, and Z. Ikonić, “Optimization of intersubband resonant second-order susceptibility in assymetric graded AlxGa1−xAs quantum wells using supersymmetric quantum mechanics,” Phys. Rev. B 56, 1033–1036 (1997). [CrossRef]
8. Y. Yu and K. Yang, “Simulating the Wess-Zumino supersymmetry model in optical lattices,” Phys. Rev. Lett. 105, 150605 (2010). [CrossRef]
9. T. G. Tenev, P. A. Ivanov, and N. V. Vitanov, “Proposal for trapped-ion emulation of the electric dipole moment of neutral relativistic particles,” Phys. Rev. A 87, 022103 (2013). [CrossRef]
10. R. El-Ganainy, A. Eisfeld, M. Levy, and D. N. Christodoulides, “On-chip non-reciprocal optical devices based on quantum inspired photonic lattices,” Appl. Phys. Lett. 103, 161105 (2013). [CrossRef]
11. M.-A. Miri, M. Heinrich, R. El-Ganainy, and D. N. Christodoulides, “Supersymmetric optical structures,” Phys. Rev. Lett. 110, 233902 (2013). [CrossRef]
12. S. Longhi and G. Della Valle, “Transparency at the interface between two isospectral crystals,” Europhys. Lett. 102, 40008 (2013). [CrossRef]
13. C. Daskaloyannis, “Generalized deformed oscillator and nonlinear algebras,” J. Phys. A: Math. Gen. 24, 789–794 (1991). [CrossRef]
14. V. V. Dodonov, M. A. Marchiollo, Y. A. Korennoy, V. I. Man’ko, and Y. A. Moukhin, “Parametric excitation of photon-added coherent states,” Phys. Scr. 58, 469–480 (1998). [CrossRef]
15. A. A. Sukhorukov, A. S. Solntsev, and J. E. Sipe, “Classical simulation of squeezed light in optical waveguide arrays,” Phys. Rev. A 87, 053823 (2013). [CrossRef]
16. L. Infeld and T. E. Hull, “The factorization method,” Rev. Mod. Phys. 23, 21–68 (1951). [CrossRef]
17. A. L. Jones, “Coupling of optical fibers and scattering in fibers,” J. Opt. Soc. Am. 55, 261–271 (1965). [CrossRef]
19. B. M. Rodríguez-Lara, “Exact dynamics of finite Glauber-Fock photonic lattices,” Phys. Rev. A 84, 053845 (2011). [CrossRef]
20. A. Perez-Leija, R. Keil, A. Szameit, A. F. Abouraddy, H. Moya-Cessa, and D. N. Christodoulides, “Tailoring the correlation and anticorrelation behavior of path-entangled photons in Glauber-Fock lattices,” Phys. Rev. A 85, 013848 (2012). [CrossRef]
21. B. M. Rodríguez-Lara, F. Soto-Eguibar, A. Z. Cárdenas, and H. M. Moya-Cessa, “A classical simulation of nonlinear Jaynes-Cummings and Rabi models in photonic lattices,” Opt. Express 21, 12888–128981 (2013). [CrossRef] [PubMed]
22. M. Abramowitz and I. A. Stegun, Handbook of Mathematical Functions(Dover1970).
23. B. M. Rodríguez-Lara, H. M. Moya-Cessa, and D. N. Christodoulides, “Propagation, perfect transmission and trapping in three-waveguide axially varying couplers,” arXiv:1310.4754 [physics.optics] (2013).
24. R. R. Puri and G. S. Agarwal, “Unitarily inequivalent classes of minimum uncertainty states of SU(1,1),” Int. J. Mod. Phys. B 10, 1563–1572 (1996). [CrossRef]
25. I. S. Gradshteyn and I. M. Ryzhik, Table of Integrals, Series and Products (Academic, 2007).