| 1. |
- Björk, Gunnar G., et al.
(författare)
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Limits to the efficiency of quantum lithography
- 2011
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Ingår i: Conf. Lasers Electro-Opt. Europe Eur. Quantum Electron. Conf., CLEO EUROPE/EQEC. - 9781457705335 ; , s. 5943416-
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Konferensbidrag (refereegranskat)abstract
- Quantum lithography promises, in principle, unlimited feature resolution, independent of wavelength. The price to be paid is that the lithographic film must consist of a multi-photon absorbing material. If N photons are absorbed, the minimum feature resolution goes from roughly /2 to /2N. However, there has been a discussion in the literature as to what is the probability of N photons in a lithographic exposure field to hit the same detector pixel, thereby enabling the needed N-photon absorption. On one hand it has been claimed that If the optical system is aligned properly, the probability of the first photon arriving in a small absorptive volume of space time is proportional to [the field intensity]. However, the remaining N-1 photons are constrained to arrive at the same place at the same time [1]. On the other hand it has been argued that it is not true that the first arriving photon greatly constrains the arrival location of the following ones Very few photons will be absorbed in one point since they typically arrive far apart. [2]. The answer to this dispute dictate very much the practical feasibility of quantum lithography, because if the few photons in the entangled state are spread out over the exposed area, the probability will quickly become negligible that they arrive at the same spot (causing a N-photon detection event). This will render quantum lithography very inefficient, albeit still feasible in principle.
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| 2. |
- Kothe, Christian, 1980-
(författare)
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Applications and characterisation of correlations in quantum optics
- 2011
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Quantum optics offers a huge variety of exciting phenomena. Many of them are still in their infancy and especially when it comes to implementing devices using these effects for more than a proof of principle demonstration still many things have to be investigated and understood. In this thesis I discuss the role of correlations in some areas of quantum optics and in some cases compare it to classical optics. Four papers form the core of the thesis. In the first paper, I propose a new measure for entanglement. This measure is based on correlations between two states. I show, how this measure relates to another measure, the concurrence. It turns out that the measure is a bijective map of the concurrence for a pure state of two qubits. I motivate why the new measure is useful if one wants to implement it experimentally. I discuss its behaviour for the case of two qubits and show its properties when dealing with pure and with mixed states. The second paper extends the result of the first one to the case where one has higher-dimensional states than qubits. In the third paper I look at phase super-resolution. I show that it can be interpreted as a purely classical effect and I analyse what is needed and what is not needed to achieve it. Specifically, I show that quantum correlations in terms of entanglement is not needed to demonstrate phase super-resolution. By doing so I propose how one could achieve arbitrarily high phase super-resolution. Finally, the last paper looks at the efficiency of quantum lithography and quantum imaging. It shows, that some basic assumptions in the original proposals of quantum lithography seems unfounded and that, as a consequence, the efficiency is poor. I give formulæ for the explicit scaling behaviour when changing the number of photons in a mode or when changing the number of pixels. The effect of the results on the future of quantum lithography is discussed as well.
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| 3. |
- Kothe, Christian, et al.
(författare)
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Arbitrarily high super-resolving phase measurements at telecommunication wavelengths
- 2010
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Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 81:6, s. 63836-
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Tidskriftsartikel (refereegranskat)abstract
- We present two experiments that achieve phase super-resolution at telecommunication wavelengths. One of the experiments is realized in the space domain and the other is realized in the time domain. Both experiments show high visibility and are performed with standard lasers and single-photon detectors. The first experiment uses six-photon coincidences, whereas the latter experiment needs no coincidence measurements, is easy to perform, and achieves, in principle, arbitrarily high phase super-resolution. Here, we demonstrate a 30-fold increase of the resolution. We stress that neither entanglement nor joint detection is needed in these experiments, which demonstrates that neither is necessary to achieve phase super-resolution.
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| 4. |
- Kothe, Christian, et al.
(författare)
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Detecting entanglement through correlations between local observables
- 2007
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Ingår i: Journal of Physics, Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 84, s. 012010-
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Tidskriftsartikel (refereegranskat)abstract
- We propose a measure of two-qubit entanglement that is invariant under local unitary transformations, and which is based on local measurements covariances. It measures the Hilbert-Schmidt distance between the state and the product state obtained by multiplying the local density matrices. The measure has the benefit that the experimentalist need not have any a priori knowledge of the state to make the measurements. For pure states, the measure provides the state's concurrence directly, without resorting to state tomography. For statistically mixed states, the measure provides bounds for the concurrence. The two-qutrit case is also studied.
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| 5. |
- Kothe, Christian, et al.
(författare)
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Entanglement quantification through local observable correlations
- 2007
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Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 75:1
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Tidskriftsartikel (refereegranskat)abstract
- We present a significantly improved scheme of entanglement detection inspired by local uncertainty relations for a system consisting of two qubits. Developing the underlying idea of local uncertainty relations, namely correlations, we demonstrate that it is possible to define a measure which is invariant under local unitary transformations and which is based only on local measurements. It is quite simple to implement experimentally and it allows entanglement quantification in a certain range for mixed states and exactly for pure states, without first obtaining full knowledge (e.g., through tomography) of the state.
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| 6. |
- Kothe, Christian, et al.
(författare)
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Experimental determination of the degree of polarization of quantum states
- 2013
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Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 87:4, s. 043814-
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate experimental excitation-manifold-resolved polarization characterization of quantum states of light ranging from the few-photon to the many-photon level. In contrast to the traditional characterization of polarization that is based on the Stokes parameters, we experimentally determine the Stokes vector of each excitation manifold separately. Only for states with a given photon number do the methods coincide. For states with an indeterminate photon number, for example Gaussian states, the employed method gives a richer and more accurate description. We apply the method both in theory and in experiment to some common states to demonstrate its advantages.
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| 7. |
- Kothe, Christian, et al.
(författare)
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On the efficiency of quantum lithography
- 2011
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Ingår i: New Journal of Physics. - : IOP Publishing. - 1367-2630. ; 13, s. 043028-
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Tidskriftsartikel (refereegranskat)abstract
- Quantum lithography promises, in principle, unlimited feature resolution, independent of wavelength. However, in the literature, at least two different theoretical descriptions of quantum lithography exist. They differ in the extent to which they predict that the photons retain spatial correlation from generation to absorption, and although both predict the same feature size, they vastly differ in predicting how efficiently a quantum lithographic pattern can be exposed. Until recently, essentially all quantum lithography experiments have been performed in such a way that it is difficult to distinguish between the two theoretical explanations. However, last year an experiment was performed that gives different outcomes for the two theories. We comment on the experiment and show that the model that fits the data unfortunately indicates that the trade-off between resolution and efficiency in quantum lithography is very unfavourable.
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| 8. |
- Sainz, Isabel, et al.
(författare)
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Estimating entanglement through local correlations
- 2007
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Ingår i: ICONO 2007: Physics Of Intense And Superintense Laser Fields; Attosecond Pulses; Quantum And Atomic Optics; And Engineering Of Quantum Information. - : SPIE. - 9780819468833 ; , s. E7263-E7263
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Konferensbidrag (refereegranskat)abstract
- A bipartite, arbitrary-dimensional entanglement measure based on local correlations of any set of generators of the corresponding algebras is proposed. An explicit relation with the I- and 3-concurrences for pure states, and a limit for entangled mixed states, are given.
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