A 2022-es fizikai Nobel-díjat a francia Alain Aspect, az amerikai John F. Clauser és az osztrák A... more A 2022-es fizikai Nobel-díjat a francia Alain Aspect, az amerikai John F. Clauser és az osztrák Anton Zeilinger kapta az összefonódott fotonokkal végzett kísérleteikért, a Bell-egyenlőtlenségek megsértésének megállapításáért és a kvantuminformatika területén végzett úttörő munkásságukért. Ebben a cikkben megismertetjük az olvasót a kvantumfizika egyik legérdekesebb jelenségével, az összefonódással, amely számos kvantuminformatikai és kvantumkommunikációs alkalmazás alapegysége. Bemutatjuk a három Nobel-díjas fizikus kapcsolódó munkásságát, és kitérünk néhány olyan kvantuminformatikai területre és alkalmazásra, ahol az összefonódás fontos szerepet tölt be.
The results of a series of pump–probe spectral hole-burning experiments are presented on Yb3+- or... more The results of a series of pump–probe spectral hole-burning experiments are presented on Yb3+- or Er3+-doped Li6Y(BO3)3 (LYB) single crystals in the temperature range of 2–14 K and 9–28 K, respectively. The spectral hole has a complex structure for Yb3+ with superposed narrow and broad bands, while a single absorption hole has been observed for Er3+. Population relaxation times (T1) at about 850 ± 60 μs and 1010 ± 50 μs and dipole relaxation times (T2) with values of 1100 ± 120 ns and 14.2 ± 0.3 ns have been obtained for the two components measured for the Yb3+:2F7/2—2F5/2 transition. T1 = 402 ± 8 μs and T2 = 11.9 ± 0.2 ns values have been found for the Er3+:4I15/2—4I11/2 excitation. The spectral diffusion rate at about 1 and 5 MHz/ms has been determined for the narrow and broad spectral line in Yb3+-doped crystal, respectively. The temperature dependence of the spectral hole halfwidth has also been investigated.
Kangwei Xia, ∗ Fiammetta Sardi, † Colin Sauerzapf, Thomas Kornher, Hans-Werner Becker, Zsolt Kis,... more Kangwei Xia, ∗ Fiammetta Sardi, † Colin Sauerzapf, Thomas Kornher, Hans-Werner Becker, Zsolt Kis, Laszlo Kovacs, Roman Kolesov, and Jörg Wrachtrup 4 3. Physikalisches Institut, University of Stuttgart, 70569 Stuttgart, Germany RUBION, Ruhr-Universität Bochum, 44780 Bochum, Germany Wigner Research Center for Physics, Institute for Solid State Physics and Optics, H-1121 Budapest, Hungary Max Planck Institute for Solid State Research, 70569 Stuttgart, Germany (Dated: April 2, 2021)
2016 24th European Signal Processing Conference (EUSIPCO), 2016
Security of the communications could be ensured using cryptography protocols. While asymmetrical ... more Security of the communications could be ensured using cryptography protocols. While asymmetrical protocols can be cracked using quantum computers, the symmetrical protocols stand against quantum attacks. However, the keys need to be exchanged in a secure way. A method is offered by the quantum key distribution (QKD) protocols. The QKD system should operate close to the fundamental quantum noise level. A possible attack is to steal some photons during the communication, but every change will result in some excess noise. This is why it is important to know the base noise level of the system, and every possible solutions need to be considered to reduce the noise of the system. To foster the research in this field, we started to develop a second generation QKD system over a 16 km long single mode, ordinary telecommunications fiber and focused on noise reduction.
Nowadays, widely spread encryption methods (e.g., RSA) and protocols enabling digital signatures ... more Nowadays, widely spread encryption methods (e.g., RSA) and protocols enabling digital signatures (e.g., DSA, ECDSA) are an integral part of our life. Although recently developed quantum computers have low processing capacity, huge dimensions and lack of interoperability, we must underline their practical significance – applying Peter Shor’s quantum algorithm (which makes it possible to factorize integers in polynomial time) public key cryptography is set to become breakable. As an answer, symmetric key cryptography proves to be secure against quantum based attacks and with it quantum key distribution (QKD) is going through vast development and growing to be a hot topic in data security. This is due to such methods securely generating symmetric keys by protocols relying on laws of quantum physics.
Nonlinear diffuse femtosecond-pulse reflectometry is introduced as a powerful experimental tool f... more Nonlinear diffuse femtosecond-pulse reflectometry is introduced as a powerful experimental tool for the unambiguous characterization of polar and non-polar point symmetry groups of harmonic upconversion nanoparticles. Using intense ultrashort 40 femtosecond laser pulses and an appropriate figure of merit (FOM), second and third harmonic emission serve for the structural characterization of polar Yb-doped lithium niobate and non-polar titanium dioxide nanoparticles. The tool is capable of differentiating these two samples by FOM values that differ by up to 13 orders of magnitude. The general applicability to harmonic upconversion nanoparticles over a broad range of intensities and wavelength spectrum, is discussed.
It is shown that the classical and quantum mechanical description of first and second order nonli... more It is shown that the classical and quantum mechanical description of first and second order nonlinear optical processes (including squeezing) are equivalent to the effect that in both cases an initial phase space distribution is transformed in the same manner. Three-photon states – star states – are generated in third order nonlinear processes, where the classical and quantum descriptions give essentially different results. It is pointed out that the efficiency of the star state in a three photon process is superior to that of a coherent state with two order of magnitude.
International Journal of Theoretical Physics, 2008
... E. Wu ( ) · LX Zeng · XA Zhang Physics Department, Xianyang Normal University, Xianyang 71200... more ... E. Wu ( ) · LX Zeng · XA Zhang Physics Department, Xianyang Normal University, Xianyang 712000, People's Republic of China e-mail ... are essentially described by continuous variables (CV) and CV quantum information provides an interesting alternative to the tra-ditional qubit ...
ABSTRACT We present two methods for the controlled creation of entangled exciton states in a lase... more ABSTRACT We present two methods for the controlled creation of entangled exciton states in a laser-driven system of two identical quantum dots interacting via an energy-transfer process. The first method uses rotation of the two-particle states and is used for the creation of entanglement between the vacuum state and the biexciton state. The second method is based on adiabatic passage techniques and is used for the creation of a single-exciton entangled state.
We introduce a novel procedure for qubit rotation, alternative to the commonly used method of Rab... more We introduce a novel procedure for qubit rotation, alternative to the commonly used method of Rabi oscillations of controlled pulse area. It is based on the technique of Stimulated Raman Adiabatic Passage (STIRAP) and therefore it is robust against fluctuations of experimental parameters. Furthermore, our work shows that it is in principle possible to perform quantum logic operations via stimulated Raman adiabatic passage. This opens up the search for a completely new class of schemes to implement logic gates.
The vibrational state of a polyatomic molecule excited with a transform limited light pulse is de... more The vibrational state of a polyatomic molecule excited with a transform limited light pulse is determined analytically. We analyze how the properties of the vibrational state depend on the duration of the exciting pulse and the possible geometrical configurations of the nuclear potential surfaces. It is pointed out that a finite exciting pulse results in an entangled vibrational state. The
Acta Physica Hungarica B Quantum Electronics, Apr 1, 2005
A robust method utilizing a combination of optical pumping and a series of coherent excitation pr... more A robust method utilizing a combination of optical pumping and a series of coherent excitation processes is developed for preparing any pure and a wide class of mixed quantum states in the decoherence-free ground-state subspace of a degenerate four-state system. For a given pulse sequence the same final state is obtained regardless of the initial state of the system. An example is presented where a pure state is prepared by a series of excitation processes in the two-dimensional dark subspace of the atom.
ABSTRACT We have looked at the laser-induced excitation of a level manifold coupled through a sin... more ABSTRACT We have looked at the laser-induced excitation of a level manifold coupled through a single excited level. This generalizes the ordinary Λ configuration to many levels. It is the original situation where stimulated Raman adiabatic passage (STIRAP) has been considered. We then apply optimal control theory to determine the pulse sequence which effects a predetermined superposition state with a minimal involvement of the excited state. The program is free to find its optimal pulse sequence, and we find that a generalization of the ordinary counterintuitive situation emerges. In addition to verifying the efficiency of the counterintuitive approach, the work justifies the separation into dark and bright subspaces, where time evolution in the former has to include the dynamical effects of adiabatic corrections.
A 2022-es fizikai Nobel-díjat a francia Alain Aspect, az amerikai John F. Clauser és az osztrák A... more A 2022-es fizikai Nobel-díjat a francia Alain Aspect, az amerikai John F. Clauser és az osztrák Anton Zeilinger kapta az összefonódott fotonokkal végzett kísérleteikért, a Bell-egyenlőtlenségek megsértésének megállapításáért és a kvantuminformatika területén végzett úttörő munkásságukért. Ebben a cikkben megismertetjük az olvasót a kvantumfizika egyik legérdekesebb jelenségével, az összefonódással, amely számos kvantuminformatikai és kvantumkommunikációs alkalmazás alapegysége. Bemutatjuk a három Nobel-díjas fizikus kapcsolódó munkásságát, és kitérünk néhány olyan kvantuminformatikai területre és alkalmazásra, ahol az összefonódás fontos szerepet tölt be.
The results of a series of pump–probe spectral hole-burning experiments are presented on Yb3+- or... more The results of a series of pump–probe spectral hole-burning experiments are presented on Yb3+- or Er3+-doped Li6Y(BO3)3 (LYB) single crystals in the temperature range of 2–14 K and 9–28 K, respectively. The spectral hole has a complex structure for Yb3+ with superposed narrow and broad bands, while a single absorption hole has been observed for Er3+. Population relaxation times (T1) at about 850 ± 60 μs and 1010 ± 50 μs and dipole relaxation times (T2) with values of 1100 ± 120 ns and 14.2 ± 0.3 ns have been obtained for the two components measured for the Yb3+:2F7/2—2F5/2 transition. T1 = 402 ± 8 μs and T2 = 11.9 ± 0.2 ns values have been found for the Er3+:4I15/2—4I11/2 excitation. The spectral diffusion rate at about 1 and 5 MHz/ms has been determined for the narrow and broad spectral line in Yb3+-doped crystal, respectively. The temperature dependence of the spectral hole halfwidth has also been investigated.
Kangwei Xia, ∗ Fiammetta Sardi, † Colin Sauerzapf, Thomas Kornher, Hans-Werner Becker, Zsolt Kis,... more Kangwei Xia, ∗ Fiammetta Sardi, † Colin Sauerzapf, Thomas Kornher, Hans-Werner Becker, Zsolt Kis, Laszlo Kovacs, Roman Kolesov, and Jörg Wrachtrup 4 3. Physikalisches Institut, University of Stuttgart, 70569 Stuttgart, Germany RUBION, Ruhr-Universität Bochum, 44780 Bochum, Germany Wigner Research Center for Physics, Institute for Solid State Physics and Optics, H-1121 Budapest, Hungary Max Planck Institute for Solid State Research, 70569 Stuttgart, Germany (Dated: April 2, 2021)
2016 24th European Signal Processing Conference (EUSIPCO), 2016
Security of the communications could be ensured using cryptography protocols. While asymmetrical ... more Security of the communications could be ensured using cryptography protocols. While asymmetrical protocols can be cracked using quantum computers, the symmetrical protocols stand against quantum attacks. However, the keys need to be exchanged in a secure way. A method is offered by the quantum key distribution (QKD) protocols. The QKD system should operate close to the fundamental quantum noise level. A possible attack is to steal some photons during the communication, but every change will result in some excess noise. This is why it is important to know the base noise level of the system, and every possible solutions need to be considered to reduce the noise of the system. To foster the research in this field, we started to develop a second generation QKD system over a 16 km long single mode, ordinary telecommunications fiber and focused on noise reduction.
Nowadays, widely spread encryption methods (e.g., RSA) and protocols enabling digital signatures ... more Nowadays, widely spread encryption methods (e.g., RSA) and protocols enabling digital signatures (e.g., DSA, ECDSA) are an integral part of our life. Although recently developed quantum computers have low processing capacity, huge dimensions and lack of interoperability, we must underline their practical significance – applying Peter Shor’s quantum algorithm (which makes it possible to factorize integers in polynomial time) public key cryptography is set to become breakable. As an answer, symmetric key cryptography proves to be secure against quantum based attacks and with it quantum key distribution (QKD) is going through vast development and growing to be a hot topic in data security. This is due to such methods securely generating symmetric keys by protocols relying on laws of quantum physics.
Nonlinear diffuse femtosecond-pulse reflectometry is introduced as a powerful experimental tool f... more Nonlinear diffuse femtosecond-pulse reflectometry is introduced as a powerful experimental tool for the unambiguous characterization of polar and non-polar point symmetry groups of harmonic upconversion nanoparticles. Using intense ultrashort 40 femtosecond laser pulses and an appropriate figure of merit (FOM), second and third harmonic emission serve for the structural characterization of polar Yb-doped lithium niobate and non-polar titanium dioxide nanoparticles. The tool is capable of differentiating these two samples by FOM values that differ by up to 13 orders of magnitude. The general applicability to harmonic upconversion nanoparticles over a broad range of intensities and wavelength spectrum, is discussed.
It is shown that the classical and quantum mechanical description of first and second order nonli... more It is shown that the classical and quantum mechanical description of first and second order nonlinear optical processes (including squeezing) are equivalent to the effect that in both cases an initial phase space distribution is transformed in the same manner. Three-photon states – star states – are generated in third order nonlinear processes, where the classical and quantum descriptions give essentially different results. It is pointed out that the efficiency of the star state in a three photon process is superior to that of a coherent state with two order of magnitude.
International Journal of Theoretical Physics, 2008
... E. Wu ( ) · LX Zeng · XA Zhang Physics Department, Xianyang Normal University, Xianyang 71200... more ... E. Wu ( ) · LX Zeng · XA Zhang Physics Department, Xianyang Normal University, Xianyang 712000, People's Republic of China e-mail ... are essentially described by continuous variables (CV) and CV quantum information provides an interesting alternative to the tra-ditional qubit ...
ABSTRACT We present two methods for the controlled creation of entangled exciton states in a lase... more ABSTRACT We present two methods for the controlled creation of entangled exciton states in a laser-driven system of two identical quantum dots interacting via an energy-transfer process. The first method uses rotation of the two-particle states and is used for the creation of entanglement between the vacuum state and the biexciton state. The second method is based on adiabatic passage techniques and is used for the creation of a single-exciton entangled state.
We introduce a novel procedure for qubit rotation, alternative to the commonly used method of Rab... more We introduce a novel procedure for qubit rotation, alternative to the commonly used method of Rabi oscillations of controlled pulse area. It is based on the technique of Stimulated Raman Adiabatic Passage (STIRAP) and therefore it is robust against fluctuations of experimental parameters. Furthermore, our work shows that it is in principle possible to perform quantum logic operations via stimulated Raman adiabatic passage. This opens up the search for a completely new class of schemes to implement logic gates.
The vibrational state of a polyatomic molecule excited with a transform limited light pulse is de... more The vibrational state of a polyatomic molecule excited with a transform limited light pulse is determined analytically. We analyze how the properties of the vibrational state depend on the duration of the exciting pulse and the possible geometrical configurations of the nuclear potential surfaces. It is pointed out that a finite exciting pulse results in an entangled vibrational state. The
Acta Physica Hungarica B Quantum Electronics, Apr 1, 2005
A robust method utilizing a combination of optical pumping and a series of coherent excitation pr... more A robust method utilizing a combination of optical pumping and a series of coherent excitation processes is developed for preparing any pure and a wide class of mixed quantum states in the decoherence-free ground-state subspace of a degenerate four-state system. For a given pulse sequence the same final state is obtained regardless of the initial state of the system. An example is presented where a pure state is prepared by a series of excitation processes in the two-dimensional dark subspace of the atom.
ABSTRACT We have looked at the laser-induced excitation of a level manifold coupled through a sin... more ABSTRACT We have looked at the laser-induced excitation of a level manifold coupled through a single excited level. This generalizes the ordinary Λ configuration to many levels. It is the original situation where stimulated Raman adiabatic passage (STIRAP) has been considered. We then apply optimal control theory to determine the pulse sequence which effects a predetermined superposition state with a minimal involvement of the excited state. The program is free to find its optimal pulse sequence, and we find that a generalization of the ordinary counterintuitive situation emerges. In addition to verifying the efficiency of the counterintuitive approach, the work justifies the separation into dark and bright subspaces, where time evolution in the former has to include the dynamical effects of adiabatic corrections.
Uploads
Papers by Zsolt Kis