Papers by Robert J C Spreeuw
We creeren tweedimensionale roosters van ultrakoude atomen, vastgehouden boven een chip, door pat... more We creeren tweedimensionale roosters van ultrakoude atomen, vastgehouden boven een chip, door patronen te etsen in een dunne laag gemagnetiseerd materiaal. Om quantumsimulatie te realiseren willen we interacties induceren door hooggeexciteerde Rydbergniveaus aan te slaan. Anderzijds willen we ook roosters met een zodanig kleine roosterafstand realiseren dat interactie tot stand komt via sterke quantumtunneling.
Foundations of Physics
A classical analogy of quantum mechanical entanglement is presented, using classical light beams.... more A classical analogy of quantum mechanical entanglement is presented, using classical light beams. The analogy can be pushed a long way, only to reach its limits when we try to represent multiparticle, or nonlocal, entanglement. This demonstrates that the latter is of exclusive quantum nature. On the other hand, the entanglement of different degrees of freedom of the same particle might be considered classical. The classical analog cannot replace Einstein± Podolsky± Rosen type experiments, nor can it be used to build a quantum computer. Nevertheless, it does provide a reliable guide to the intuition and a tool for visualizing abstract concepts in low-dimensional Hilbert spaces.
Physical Review Letters, 2002
We report on an experiment on Grover's quantum search algorithm showing that classical waves can ... more We report on an experiment on Grover's quantum search algorithm showing that classical waves can search a N-item database as efficiently as quantum mechanics can. The transverse beam profile of a short laser pulse is processed iteratively as the pulse bounces back and forth between two mirrors. We directly observe the sought item being found in ϳ p N iterations, in the form of a growing intensity peak on this profile. Although the lack of quantum entanglement limits the size of our database, our results show that entanglement is neither necessary for the algorithm itself, nor for its efficiency.
Physical Review A, 2005
We investigate the question whether Michelson type interferometry is possible if the role of the ... more We investigate the question whether Michelson type interferometry is possible if the role of the beam splitter is played by a spontaneous process. This question arises from an inspection of trajectories of atoms bouncing inelastically from an evanescent-wave (EW) mirror. Each final velocity can be reached via two possible paths, with a spontaneous Raman transition occurring either during the ingoing or the outgoing part of the trajectory. At first sight, one might expect that the spontaneous character of the Raman transfer would destroy the coherence and thus the interference. We investigated this problem by numerically solving the Schrödinger equation and applying a Monte-Carlo wave-function approach. We find interference fringes in velocity space, even when random photon recoils are taken into account.
Optics and Spectroscopy, 2005
ABSTRACT Measurements of the radiative properties of cold 87Rb atoms close to a dielectric/vacuum... more ABSTRACT Measurements of the radiative properties of cold 87Rb atoms close to a dielectric/vacuum interface are reported. This is the first observation of a quantum-electrodynamic (QED) modification of radiative properties in vacuum near a dielectric surface. Evanescent wave (EW) spectroscopy on cold atoms that were dropped on a glass surface was used. An increase of the natural linewidth by up to 25% compared to the free space value was found. This was attributed to QED broadening and level shifts, as well as local Stark shifts near the surface. By varying the characteristic EW length, a position dependence characteristic for QED was observed. The role of transient internal dynamics of the atoms as they move through the strongly inhomogeneous EW was investigated.
Applied Physics B, 2001
We have characterized a semiconductor amplifier laser system which provides up to 200 mW output a... more We have characterized a semiconductor amplifier laser system which provides up to 200 mW output after a single-mode optical fiber at 780 nm wavelength. The system is based on a tapered semiconductor gain element, which amplifies the output of a narrow-linewidth diode laser. Gain and saturation are discussed as a function of operating temperature and injection current. The spectral properties of the amplifier are investigated with a grating spectrometer. Amplified spontaneous emission (ASE) causes a spectral background with a width of 4 nm FWHM. The ASE background was suppressed to below our detection limit by a proper choice of operating current and temperature, and by sending the light through a single-mode optical fiber. The final ASE spectral density was less than 0.1 nW/MHz, i.e. less than 0.2 % of the optical power. Related to an optical transition linewidth of Γ/2π = 6 MHz for rubidium, this gives a background suppression of better than −82 dB. An indication of the beam quality is provided by the fiber coupling efficiency up to 59 %. The application of the amplifier system as a laser source for atom optical experiments is discussed.
We introduce spontaneous decay of qubits to damp the oscillations in a single-item quantum search... more We introduce spontaneous decay of qubits to damp the oscillations in a single-item quantum search. This allows a more robust mode of operation where the readout is performed after the system has reached a steady state, rather than after a prescribed number of iterations. We show numerically for up to q = 29 qubits that, with near-unit probability, the readout yields an error-free solution after O(log q) repetitions. The huge size of the state space is dealt with by exploiting a symmetry in the master equation that reduces the scaling of computer resources from exponential to polynomial.
Physical Review A, 1992
We report on the experimental realization and theoretical analysis of four-level systems produced... more We report on the experimental realization and theoretical analysis of four-level systems produced in passive optical ring cavities by introducing various intracavity elements. Birefringent elements couple waves with different polarizations and thus lift the polarization degeneracy of the cavity modes. Reflecting elements couple waves propagating in different directions and lift the propagation degeneracy. A combination of these elements leads, in general, to a splitting of every longitudinal cavity mode into a four-mode system. Under the restriction that the optical components are loss-free, the description of these ring cavities in a transmission-matrix formalism leads in a natural way to the study of the Lie group U(2, 2) and its Lie algebra u(2, 2). We associate each of the 16 generators of this algebra with a specific type of optical element, some of which are standard components, others not. From the commutation relations of the generators, we derive a recipe for the construction of the nonstandard components as a sequence of standard ones. It follows that the entire U(2, 2) group can actually be realized. The number of independent parameters-16 for a general U(2, 2) elementis shown to be reduced substantially if the optical components are selected out of a restricted number of types, provided that the corresponding generators define a subalgebra of u(2, 2). In such cases, a subgroup of U(2, 2) is realized and the number of independent parameters of the optical system is given by the number of generators of the subalgebra. A connection is established between the subalgebras and symmetry properties of the optical components in the cavity. We consider the influence of symmetries on the mode structure and consider our experimental results from this viewpoint. In particular, we discuss time-reversal invariance, leading to the symplectic group USp(2, 2), and we identify antiunitary symmetries leading to Kramers s degeneracy in the mode spectrum. We propose the application of the group U(2,2) in optics as a tool yielding direct practical results.
Progress in Crystal Growth and Characterization of Materials, 1996
We discuss the prospects for a laser-like source of atoms where-in close analogy to the laser, an... more We discuss the prospects for a laser-like source of atoms where-in close analogy to the laser, and in close analogy to the recently observed Bose-Einstein condensation-many atoms of an atomic gas occupy a single center-of-mass motional state. We develop a theoretical description borrowing concepts from many-body quantum field theory and laser theory. Our results show threshold behavior, mode competition and Poissonian atom statistics above threshold.
Foundations of Quantum Mechanics, 1992
Recent Developments in Quantum Optics, 1993
In recent years optics has become a popular playground for testing of basic quantum mechanical co... more In recent years optics has become a popular playground for testing of basic quantum mechanical concepts. Here we refer to questions dealing with quantum mechanical measurement theory and with the transition between quantum physics and classical physics [l] –[5]. In this paper we discuss classical optical experiments displaying features which are usually associated with quantum physics. Our favorite optical system in this context is the optical ring resonator. The static properties of such a resonator are reviewed in Section 2, in the language of coupled-mode theory. Dynamical properties are reviewed in Section 3; this includes phenomena such as Rabi oscillations, Zener tunneling, Bloch oscillations, multiphoton transitions and the Bloch-Siegert shift. The experimental results reviewed in Sections 2 and 3 establish in a sense the bona fide character and practical convenience of our model system. An important advantage of the macroscopic nature of the system is that all parameters are accessible to direct experimental control, including parameters that in the equivalent microscopic quantum system would be difficult or impossible to vary. Finally, in section 4 we give an outlook on further possibilities.
EQEC 96 1996 European Quantum Electronic Conference EQEC-96, 1996
Analogies in Optics and Micro Electronics, 1990
ABSTRACT
Coherence and Quantum Optics VI, 1990
Inherent to wave propagation in a periodic medium is the formation of band structure in the dispe... more Inherent to wave propagation in a periodic medium is the formation of band structure in the dispersion relation. As an example, when electrons with energy E and wavevector k propagate in a periodic lattice, electronic band structure E(k) results; this is one of the basic concepts of solid state physics. As another example, band structure of electromagnetic radiation, ω(k), is well known for light propagating in a dielectric medium having a one-dimensional microscopic periodicity (‘multilayer dielectric mirror’); an extension thereof to the three-dimensional case has been speculated upon1.
Progress in Optics, 1993
Publisher Summary This chapter describes the optical atoms. A particular analogous system is form... more Publisher Summary This chapter describes the optical atoms. A particular analogous system is formed by two (or four) coupled optical modes, called an “optical atom.” The optical atom allows exact realization of popular model Hamiltonians of quantum optics, and thus allows “ideal” experiments. The attraction and convenience of the system is its macroscopic nature, which allows precise control of all parameters over the ranges that are sometimes not accessible in the case of real atoms. The driven optical ring resonator forms a system for simulating resonance physics of microscopic systems. An important advantage of the macroscopic nature of this system is that, all parameters are accessible to direct experimental control, including those in which the corresponding microscopic quantum system would be difficult or impossible to vary. The chapter establishes the analogy between a quantum two-level atom and the classical limit of two coupled optical modes (optical atom). The optical band structure and four-level systems are explained. The chapter discusses two-level systems and their dynamical behavior if one of the system parameters is modulated. Some future experimental possibilities for the optical atom as a model for microscopic systems are reviewed.
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Papers by Robert J C Spreeuw