arXiv subjects

Pedro Sancho

Publications and source records attributed to Pedro Sancho.

At least 37 records · Page 2Linked to original sources

arXiv2017

Entanglement, identity and disentanglement in two-atom spontaneous emission

Two recent experiments studying the potential effect of entanglement on the emission properties of excited atoms produced in molecular photodissociation have been interpreted in conflicting ways. We present a theoretical analysis of the problem, showing that the experimental results can be explained by a combination of three processes: entanglement, exchange effects associated with the identical nature of the atoms and disentanglement by spontaneous emission. According to our approach these experiments provide the first verification of the phenomenon of disentanglement by spontaneous emission.

quant-ph↗

arXiv2016

Atomic absorption and emission in non-product states

The properties of non-product states, both (anti)symmetrized and entangled, have been extensively studied in the literature. In this paper, by extending previous partial results, we introduce a general framework to describe atomic absorption and emission in these states. Our approach shows the existence of some fundamental differences between entanglement and (anti)symmetrization and between absorption and emission. For instance, modifications of the emission properties with respect to that of uncorrelated systems occur for any (anti)symmetrized state but only for some very specific entangled states.

quant-ph↗

arXiv2016

Probing the electron charge distribution via Kapitza-Dirac diffraction

We analyze the diffraction of elementary systems as the electron by light gratings when they are described by charge distributions instead of the usual point-like form. The treatment of the problem is based on the introduction, in analogy with atomic polarizability, of state-dependent non-permanent multi-pole moments for the charge. The diffraction patterns can provide bounds on these moments. With this approach we can experimentally explore some aspects of the interpretation of the wave picture of single charges.

quant-ph↗

arXiv2015

Reflexive functors in Algebraic Geometry

Reflexive functors of modules naturally appear in Algebraic Geometry. In this paper we define a wide and elementary family of reflexive functors of modules, closed by tensor products and homomorphisms, in which Algebraic Geometry can be developed.

math.AG↗

arXiv2015

Diffraction of entangled particles by light gratings

We analyze the diffraction regime of the Kapitza-Dirac effect for particles entangled in momentum. The detection patterns show two-particle interferences. In the single-mode case we identify a discontinuity in the set of joint detection probabilities, associated with the disconnected character of the space of non-separable states. For Gaussian multi-mode states we derive the diffraction patterns, providing an example of the dependence of the light-matter interaction on entanglement. When the particles are identical, we can explore the relation between exchange and entanglement effects. We find a complementary behavior between overlapping and Schmidt's number. In particular, symmetric entanglement can cancel the exchange effects.

quant-ph↗

arXiv2014

The two-particle two-slit experiment

Identical two-particle interferometry provides a scenario where interference and exchange effects manifest at once. We present a detailed calculation of the detection patterns in the two-particle two-slit experiment by extending Feynman's Gaussian slit approach to multi-mode states. We show the existence of two regimes depending on the mode distributions. In one of them we find a novel behavior for bosons, with detection patterns almost equal to those of distinguishable particles although the overlapping is large. As a byproduct of our analysis we conclude that the interaction at the diffraction grating is an efficient method to increase the initial overlapping. We propose a scheme, within the reach of present day technology, to experimentally verify our results.

quant-ph↗

arXiv2013

Atomic Kapitza-Dirac effect with quadrupole transitions

Interactions between atoms and light fields are usually described in the electric-dipole approximation. We show that electric-quadrupole terms are important in the Kapitza-Dirac arrangement for light gratings on resonance with a quadrupole atomic transition. We derive the diffraction patterns, which in some cases are experimentally verifiable with the same techniques used with dipole transitions.

quant-ph↗

arXiv2013

Absorption properties of identical atoms

Emission rates and other optical properties of multiparticle systems in collective and entangled states differ from those in product ones. We show the existence of similar effects in the absorption probabilities for (anti)symmetrized states of two identical atoms. The effects strongly depend on the overlapping between the atoms and differ for bosons and fermions. We propose a viable experimental verification of these ideas.

quant-ph↗

arXiv2013

Atomic diffraction by light gratings with very short wavelengths

Lasers with wavelengths of the order of the atomic size are becoming available. We explore the behavior of light-matter interactions in this emergent field by considering the atomic Kapitza-Dirac effect. We derive the diffraction patterns, which are in principle experimentally testable. From a fundamental point of view, our proposal provides an example of system where the periodicity of the diffraction grating is comparable to the size of the diffracted object.

quant-ph↗

arXiv2011

A scheme for symmetrization verification

We propose a scheme for symmetrization verification in two-particle systems, based on one-particle detection and state determination. In contrast to previous proposals, it does not follow a Hong-Ou-Mandel-type approach. Moreover, the technique can be used to generate superposition states of single particles.

quant-ph↗

arXiv2011

The Bragg regime of the two-particle Kapitza-Dirac effect

We analyze the Bragg regime of the two-particle Kapitza-Dirac arrangement, completing the basic theory of this effect. We provide a detailed evaluation of the detection probabilities for multi-mode states, showing that a complete description must include the interaction time in addition to the usual dimensionless parameter w. The arrangement can be used as a massive two-particle beam splitter. In this respect, we present a comparison with Hong-Ou-Mandel-type experiments in quantum optics. The analysis reveals the presence of dips for massive bosons and a differentiated behavior of distinguishable and identical particles in an unexplored scenario. We suggest that the arrangement can provide the basis for symmetrization verification schemes.

quant-ph↗

arXiv2011

Comment on "Effect of entanglement on the decay dynamics of a pair of H(2p) atoms due to spontaneous emission"

Tanabe et al (Phys. Rev. A {\bf 82} 040101(R) 2010) have experimentally demonstrated that the emission properties of unstable atoms in entangled and product states are different. The authors define an apparent decay time as a fitting parameter which falls below the lifetime of the single atom for entangled pairs. We argue that their results about coincidence time spectra are correct, but those concerning lifetimes cannot be considered conclusive because they assume the emission of photons by the two atoms to be independent processes, a doubtful hypothesis for entangled states. We suggest an improved evaluation of the lifetimes based on a rigorous approach, which demands some modifications of the experimental procedure.

quant-ph↗

arXiv2010

Two-particle Kapitza-Dirac diffraction

We extend the study of Kapitza-Dirac diffraction to the case of two-particle systems. Due to the exchange effects the shape and visibility of the two-particle detection patterns show important differences for identical and distinguishable particles. We also identify a novel quantum statistics effect present in momentum space for some values of the initial particle momenta, which is associated with different numbers of photon absorptions compatible with the final momenta.

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arXiv2010

Identical two-particle interferometry in diffraction gratings

We study diffraction and interference of indistinguishable particles. We consider some examples where the wavefunctions and detection probabilities can be evaluated in an analytical way. The diffraction pattern of a two-particle system shows notorious differences for the cases of bosons, fermions and distinguishable particles. In the example of near-field interferometry, the exchange effects for two-fermion systems lead to the existence of planes at which the probability of double detection is null. We also discuss the relation with the approach to systems of identical particles based on correlation functions. In particular, we shall see that these functions reflect, as in noise interferometry, the underlying periodic structure of the diffraction grating.

quant-ph↗

arXiv2009

A Characterization of Linearly Semisimple Groups

Let $G = Spec A$ be an affine $K$-group scheme and $\tilde{A} = \{w \in A*: dim_K A^* \cdot w \cdot A^* < \infty \}$. Let $< -,-> : A^* \times \tilde{A} \to K, (w,\tilde{w}) := tr(w \tilde{w})$, be the trace form. We prove that $G$ is linearly reductive if and only if the trace form is non-degenerate on $A^*$.

math.AG↗

arXiv2009

Reynolds Operator on functors

Let $G= {\rm Spec} A$ be an affine $R$-monoid scheme. We prove that the category of dual functors (over the category of commutative $R$-algebras) of $G$-modules is equivalent to the category of dual functors of ${\mathcal A}^*$-modules. We prove that $G$ is invariant exact if and only if $A^*= R \times B^*$ as $R$-algebras and the first projection $A^* \to R$ is the unit of $A$. If $\mathbb M$ is a dual functor of $G$-modules and $w_G := (1,0) \in R \times B^* = A^*$, we prove that $\mathbb M^G = w_G \cdot \mathbb M$ and $\mathbb F = w_G \cdot \mathbb M \oplus (1-w_G) \cdot \mathbb M$; hence, the Reynolds operator can defined on $\mathcal M$.

math.AG↗

arXiv2009

Entanglement of unstable atoms: modifications of the emission properties

We analyse the influence of entanglement on the emission properties of atoms. To this end, first, we propose a scheme for the preparation of a pair of entangled Helium atoms, one in the ortho and the other in the para spin configuration. We discuss a realistic scenario for this process, based in the double ionization of He by intense laser fields. These states are used to analyse disentanglement and the role of entanglement in the spontaneous emission from the pair. In particular, we show that the decaying rate of an entangled atom is different from that in a product state, modifying the temporal emission distribution and lifetime of the atoms.

quant-ph↗

arXiv2009

Correlations between the interacting fragments of decaying processes

We study the correlations (and alignment as a particular case) existent between the fragments originated in a decaying process when the daughter particles interact. The interaction between the particles is modeled using the potential of coupled oscillators, which can be treated analytically. This approach can be considered as a first step towards the characterization of realistic interacting decaying systems, an archetypal process in physics. The results presented here also suggest the possibility of manipulating correlations using external fields, a technique that could be useful to provide sources of entangled massive particles.

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