Karel Lemr

Temporal steering and security of quantum key distribution with mutually unbiased bases against individual attacks

Temporal steering, which is a temporal analog of Einstein-Podolsky-Rosen steering, refers to temporal quantum correlations between the initial and final state of a quantum system. Our analysis of temporal steering inequalities in relation to the average quantum bit error rates reveals the interplay between temporal steering and quantum cloning, which guarantees the security of quantum key distribution based on mutually unbiased bases against individual attacks. The key distributions analyzed here include the Bennett-Brassard 1984 protocol and the six-state 1998 protocol by Bruss. Moreover, we define a temporal steerable weight, which enables us to identify a kind of monogamy of temporal correlation that is essential to quantum cryptography and useful for analyzing various scenarios of quantum causality.

Liquid chromatographic separation of pregabalin and its possible impurities with fluorescence detection after postcolumn derivatization with o-phtaldialdehyde.

A rapid procedure based on direct extraction and RP-HPLC separation of pregabalin and its possible impurities with fluorescence detection has been developed. The separation conditions and parameters of derivatization reaction for postcolumn derivatization of pregabalin with o-phtaldialdehyde/2-mercaptoethanol were studied. Purospher STAR RP-8e column with isocratic elution was employed. Fluorescence detection was performed at excitation and emission wavelength of 345 nm and 450 nm, respectively. The proposed method has an advantage of a simple sample pre-treatment and a quick and very sensitive HPLC method. The applicability of developed method was successfully verified during analysis of commercial samples of tablets of Lyrica (Pfizer, USA).

Nano-desorption electrospray and kinetic method in chiral analysis of drugs in whole human blood samples

A home-made nano-desorption electrospray ionization (nano-DESI) device and the kinetic method were tested in chiral analysis of model clinical samples containing enantiomers of one of three pharmaceutically important compounds: dihydroxyphenylalanine (DOPA), ephedrine and ibuprofen. The initial evaluation of chiral systems was carried out by direct infusion of solution mixtures (analyte/central metal/chiral reference ligand) to a standard electrospray ionization (ESI) source. Cu(II) was used as a central metal for all analytes, l-phenylalanine was applied as a chiral reference ligand for DOPA, whereas l-tryptophan was used for the other two analytes. Then, the ESI source was substituted by a nano-DESI source and dried spots of 1 μL samples of whole human blood spiked with individual drugs were successfully analyzed without any pre-treatment. Irrespective of a laborious initial nano-DESI set-up, the combination of the kinetic method with nano-desorption electrospray has, for the first time, been demonstrated as a promising tool for chiral analysis of drugs in blood samples.

Quantifying entanglement of a two-qubit system via measurable and invariant moments of its partially transposed density matrix

We describe a direct method to determine the negativity of an arbitrary two-qubit state in experiments. The method is derived by analyzing the relation between the purity, negativity, and a universal entanglement witness for two-qubit entanglement. We show how the negativity of a two-qubit state can be calculated from just three experimentally accessible moments of the partially transposed density matrix of a two-photon state. Moreover, we show that the negativity can be given as a function of only six invariants, which are linear combinations of nine invariants from the complete set of 21 fundamental and independent two-qubit invariants. We analyze the relation between these moments and the concurrence for some classes of two-qubit states (including the

Linear-optical programmable quantum router

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One-state vector formalism for the evolution of a quantum state through nested Mach-Zehnder interferometers

states, as well as pure states affected by the amplitude-damping and phase-damping channels). We also discuss the possibility of using the universal entanglement witness as an entanglement measure for various classes of two-qubit states. Moreover, we analyze how noise affects the estimation of entanglement via this witness.

Method for universal detection of two-photon polarization entanglement

Abstract This paper presents a scheme for linear-optical implementation of a programmable quantum router. Polarization encoded photon qubit is coherently routed to two spatial modes according to the state of control qubits. In our implementation, the polarization state of the signal photon does not change under the routing operation. We also discuss generalization of the scheme that would allow to obtain signal dependent routing.

Experimental quantum forgery of quantum optical money

Karol Bartkiewicz, 2, ∗ Antońın Černoch, † Dalibor Jav̊urek, Karel Lemr, ‡ Jan Soubusta, and Jǐŕı Svoziĺık Faculty of Physics, Adam Mickiewicz University, PL-61-614 Poznań, Poland RCPTM, Joint Laboratory of Optics of Palacký University and Institute of Physics of Academy of Sciences of the Czech Republic, 17. listopadu 12, 771 46 Olomouc, Czech Republic Institute of Physics of Academy of Sciences of the Czech Republic, Joint Laboratory of Optics of PU and IP AS CR, 17. listopadu 50A, 772 07 Olomouc, Czech Republic (Dated: November 19, 2014)

Scanning electron microscopic imaging of surface effects in desorption and nano-desorption electrospray ionization.

Detecting and quantifying quantum entanglement of a given unknown state poses problems that are fundamentally important for quantum information processing. Surprisingly, no direct (i.e., without quantum tomography) universal experimental implementation of a necessary and sufficient test of entanglement has been designed even for a general two-qubit state. Here we propose an experimental method for detecting a collective universal witness, which is a necessary and sufficient test of two-photon polarization entanglement. It allows us to detect entanglement for any two-qubit mixed state and to establish tight upper and lower bounds on its amount. A different element of this method is the sequential character of its main components, which allows us to obtain relatively complicated information about quantum correlations with the help of simple linear-optical elements. As such, this proposal realizes a universal two-qubit entanglement test within the present state of the art of quantum optics. We show the optimality of our setup with respect to the minimal number of measured quantities.

Application of silicon nanowires and indium tin oxide surfaces in desorption electrospray ionization

Unknown quantum information cannot be perfectly copied (cloned). This statement is the bedrock of quantum technologies and quantum cryptography, including the seminal scheme of Wiesner’s quantum money, which was the first quantum-cryptographic proposal. Surprisingly, to our knowledge, quantum money has not been tested experimentally yet. Here, we experimentally revisit the Wiesner idea, assuming a banknote to be an image encoded in the polarization states of single photons. We demonstrate that it is possible to use quantum states to prepare a banknote that cannot be ideally copied without making the owner aware of only unauthorized actions. We provide the security conditions for quantum money by investigating the physically-achievable limits on the fidelity of 1-to-2 copying of arbitrary sequences of qubits. These results can be applied as a security measure in quantum digital right management.Quantum money could protect currency against cryptographic attacksTraditional cash is being gradually replaced by digital payments and transactions with digital currency, such as bitcoin. Digital transactions are currently protected by cryptographic protocols. However, these protocols are potentially susceptible to attacks using quantum factoring algorithm. If quantum factoring is implemented on quantum computers, the resulting breach of security could make today’s digital currency obsolete. It is possible, however, to replace classical digital money with so-called quantum money, i.e., sequences of quantum bits copy-protected by their quantum nature. This paper reports on the experimental quantum optical implementation of a quantum money protocol, which was experimentally tested regarding its resistance to quantum counterfeiting based on the best physically-possible copying of individual unknown quantum bits.