Browsing by Author "Lyyra, Henri"

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  • Experimental implementation of fully controlled dephasing dynamics and synthetic spectral densities
    (2018-12-01) Liu, Zhao Di; Lyyra, Henri; Sun, Yong Nan; Liu, Bi Heng; Li, Chuan Feng; Guo, Guang Can; Maniscalco, Sabrina; Piilo, Jyrki
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Engineering, controlling, and simulating quantum dynamics is a strenuous task. However, these techniques are crucial to develop quantum technologies, preserve quantum properties, and engineer decoherence. Earlier results have demonstrated reservoir engineering, construction of a quantum simulator for Markovian open systems, and controlled transition from Markovian to non-Markovian regime. Dephasing is an ubiquitous mechanism to degrade the performance of quantum computers. However, all-purpose quantum simulator for generic dephasing is still missing. Here, we demonstrate full experimental control of dephasing allowing us to implement arbitrary decoherence dynamics of a qubit. As examples, we use a photon to simulate the dynamics of a qubit coupled to an Ising chain in a transverse field and also demonstrate a simulation of nonpositive dynamical map. Our platform opens the possibility to simulate dephasing of any physical system and study fundamental questions on open quantum systems.
  • Fidelity of dynamical maps
    (2017-05-02) Tukiainen, Mikko; Lyyra, Henri; Sarbicki, Gniewomir; Maniscalco, Sabrina
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    We introduce the concept of fidelity for dynamical maps in an open quantum system scenario. We derive an inequality linking this quantity to the distinguishability of the inducing environmental states. Our inequality imposes constraints on the allowed set of dynamical maps arising from the microscopic description of system plus environment. Remarkably, the inequality involves only the states of the environment and the dynamical map of the open system and, therefore, does not rely on the knowledge of either the microscopic interaction Hamiltonian or the environmental Hamiltonian characteristic parameters. We demonstrate the power of our result by applying it to two different scenarios: quantum programming and quantum probing. In the first case, we use it to derive bounds on the dimension of the processor for approximate programming of unitaries. In the second case we present an intriguing proof-of-principle demonstration of the ability to extract information on the environment via a quantum probe without any apriori assumption on the form of the system-environment coupling Hamiltonian.
  • Interaction independent quantum probing
    (2017-07-01) Sarbicki, Gniewomir; Tukiainen, M.; Lyyra, Henri; Maniscalco, S.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    For an open quantum system we assume that we are able to set the system's environment temperature. We fix the time interval and let the system (further referred as the probing system) to evolve during this time in two different temperatures. We make a process tomography of the resulting dynamics (quantum channels "1; "2 related to the temperatures T1 and T2 respectively). We calculate then the values of fidelities for the pair of channels. We derive an inequality between the experimental data and the partition function of environment (hence the spectrum of the environment). If the inequality is not satisfied, it implies that our assumption about the spectrum of the environment is wrong. Notice that there is no dependence on the interaction terms neither on the Hamiltonian of the probing system. We show the power of this method in the following example. Consider a two-level atom passing the one-mode vacuum. We do not know the Hamiltonian of the atom (the probing system) neither the interaction mechanism. We would like to determine the frequency of the vacuum. We will show that wide range of frequencies are forbidden by the inequality.
  • Portfolio Pumping or Happy Ending: Evidence of Quarter-End Returns in Helsinki Stock Exchange
    (2019) Lyyra, Henri
     School of Business | Bachelor's thesis
  • Symmetry in the open-system dynamics of quantum correlations
    (2017-08-21) Lyyra, Henri; Karpat, Göktug; Li, Chuan-Feng; Guo, Guang-Can; Piilo, Jyrki; Maniscalco, Sabrina
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    We study the symmetry properties in the dynamics of quantum correlations for two-qubit systems in one-sided noisy channels, with respect to a switch in the location of noise from one qubit to the other. We consider four different channel types, namely depolarizing, amplitude damping, bit-flip, and bit-phase-flip channel, and identify the classes of initial states leading to symmetric decay of entanglement, non-locality and discord. Our results show that the symmetric decay of quantum correlations is not directly linked to the presence or absence of symmetry in the initial state, while it does depend on the type of correlation considered as well as on the type of noise. We prove that asymmetric decay can be used to infer, in certain cases, characteristic properties of the channel. We also show that the location of noise may lead to dramatic changes in the persistence of phenomena such as entanglement sudden death and time-invariant discord.
  • Volatility of trading volume and expected stock returns – Empirical evidence from the Finnish stock market
    (2022) Lyyra, Henri
     School of Business | Master's thesis
    The relationship between trading volume and expected stock returns has been extensively studied in the finance literature. Volatility of trading volume, on the other hand, has received much less attention, despite its significance for stock liquidity and its volatility. The high volatility of trading volume can be seen as an additional risk factor, making it very interesting as a research topic. The most significant study related to the volatility of trading volume and its effects on stock returns has been presented by Chordia, Subrahmanyam and Anshuman (2001). According to their study, U.S. stocks with high volatility of trading activity yield less than stocks with low volatility of trading activity. This observation is special because, according to traditional financial theory, the results should be reversed, in which case the investor would be compensated for the high volatility of trading volume, which can be seen as a risk factor. In their research, they use the trading volume and the share turnover ratio as measures of trading activity. This study is the first to research the same phenomenon in the Finnish stock market. My goal is to present the existence of the phenomenon in Finland for the first time with Finnish stock data and to compare the results with the above-mentioned study. I analysed data from the Refinitiv Eikon database using the methods used by Chordia, Subrahmanyam, and Anshuman (2001), mainly by Fama-Macbeth (1973) regressions, to make the study results comparable. The results of my research are significant: in my 2002–2021 time series, I present the finding that Finnish equities perform better if the volatility of trading activity is high rather than low. In addition, the results using the trading volume as a measure of trading activity are statistically significant. The observation of a positive correlation between the volatility of trading activity and stock returns is remarkable, as it is the opposite finding to that observed for U.S. equities in the above-mentioned study. My research brings new results to the existing literature on the Finnish stock market.