Joakim Bergli

• Anghel, D. V.; Dolineanu, M.; Bergli, Joakim & Maasilta, I. J. (2025). Controlling the electron-phonon heat exchange in a metallic film at sub-Kelvin temperatures by its position in a dielectric slab. Physica Scripta. ISSN 0031-8949. 100(7). doi: 10.1088/1402-4896/ade8b4. Fulltekst i vitenarkiv Vis sammendrag

  We theoretically study the heat exchange between electrons and phonons in a thin metallic film embedded in a suspended dielectric membrane, forming a layered structure in a geometry where the thickness of the membrane is much smaller than its width and length, whereas the thickness of the metallic layer is an order of magnitude smaller than the thickness of the membrane. In addition, we concentrate in the low-temperature range, where the dominant acoustic phonon wavelength is comparable to the thickness of the membrane, and where we can use the continuous elasticity theory for the phonon modes (Lamb-wave theory). Here, we extend previous studies to address how the electron-phonon heat power is influenced by the position of the metal film embedded within the insulating part of the membrane, as opposed to it being on top of the membrane. We show that the heat power can be modified by an order of magnitude just by changing the location of the metal film, and the temperature dependence of the heat power can be tuned as well, offering new ways to engineer the heat exchange and heat transport in nanodevices.

• Holm, Sverre & Bergli, Joakim (2025). Energy landscape interpretation of universal linearly increasing absorption with frequency. Journal of the Acoustical Society of America. ISSN 0001-4966. 157(2), s. 824–832. doi: 10.1121/10.0035647. Fulltekst i vitenarkiv Vis sammendrag

  Absorption of elastic waves in complex media is commonly found to increase linearly with frequency, for both longitudinal and shear waves. This ubiquitous property is observed in media such as rocks, unconsolidated sediments, and human tissue. Absorption is due to relaxation processes at the level of atomic scales and up to the sub-micron scale of biological materials. The effect of these processes is usually expressed as an integral over relaxation frequencies or relaxation times. Here, this paper argues that these processes are thermally activated. Unusually for ultrasonics and seismics, the expression for absorption from the frequency or time domains can therefore be transformed to an integral over an activation energy landscape weighted by an energy distribution. The universal power-law property surprisingly corresponds to a flat activation energy landscape. This is the solution that maximizes entropy or randomness. Therefore, the linearly increasing absorption corresponds to the energy landscape with the fewest possible constraints.

• Vistnes, Arnt Inge & Bergli, Joakim (2022). Hanbury Brown and Twiss effect demonstrated for sound waves from a waterfall: An experimental, numerical, and analytical study. American Journal of Physics (AJP). ISSN 0002-9505. 90(1), s. 20–30. doi: 10.1119/10.0006613. Fulltekst i vitenarkiv Vis sammendrag

  Hanbury Brown and Twiss determined the angular size of a visible light source (the star Sirius) by studying how the cross-correlation in intensity fluctuation recorded by two detectors changes with the distance between the detectors. We find that this principle works equally well for sound waves from a waterfall. This is remarkable, since sound is a completely different kind of wave from the HBT case. The frequency of the waves differs by a factor ∼1012 and the wavelength as well as the angular extension of the source seen from the observer's position differ by a factor ∼107. Our analysis is based on the general properties of broadband waves. We start with broadband waves at the amplitude level (not at intensity level) and demonstrate a HBT-like effect. We follow up with an explanation and demonstrations showing how the effect also manifests itself at the intensity level, providing a bridge to the original HBT work. We use the same reasoning in our numeric and analytical treatments, as well as in the experimental work, with identical results. The presentation is simple enough to be introduced even for second year bachelor students. Computer programs (in Matlab), including software for time-resolved frequency analysis, as well as original sound files are available from the authors.

• Hou, Jie; Abie, Sisay Mebre; Strand-Amundsen, Runar James; Galperin, Yuri; Bergli, Joakim & Schuelke, Christin [Vis alle 8 forfattere av denne artikkelen] (2021). Temperature dependence of the microwave dielectric properties of γ -aminobutyric acid. Scientific Reports. 11(1). doi: 10.1038/s41598-021-97178-7. Fulltekst i vitenarkiv Vis sammendrag

  The GABA molecule is the major inhibitory neurotransmitter in the mammalian central nervous system. Through binding to post-synaptic neurons, GABA reduces the neuronal excitability by hyperpolarization. Correct binding between the GABA molecules and its receptors relies on molecular recognition. Earlier studies suggest that recognition is determined by the geometries of the molecule and its receptor. We employed dielectric relaxation spectroscopy (DRS) to study the conformation and dielectric properties of the GABA molecule under physiologically relevant laboratory conditions. The dielectric properties of GABA investigated have given us new insights about the GABA molecule, such as how they interact with each other and with water molecules at different temperatures (22°C and 37.5°C). Higher temperature leads to lower viscosity, thus lower relaxation time. The change in the GABA relaxation time due to concentration change is more associated with the solution viscosity than with the GABA dipole moment. A resonance behavior was observed with high GABA concentrations at physiological temperature, where there might be a phase transition at a certain temperature for a given GABA concentration that leads to a sudden change of the dielectric properties.

• Abie, Sisay Mebre; Münch, Daniel & Bergli, Joakim (2020). Monitoring electric impedance during freezing and thawing of saline and de-ionized water. Journal of Electrical Bioimpedance. 11(1), s. 106–111. doi: 10.2478/JOEB-2020-0016. Fulltekst i vitenarkiv Vis sammendrag

  Abstract Physiological saline (0.9% NaCl) and deionized water were frozen in a laboratory chest freezer and impedance was monitored throughout freezing and thawing. The resistive and reactive components of electrical impedance were measured for these samples during freezing and thawing (heating) within a temperature range between 20 °C and −48 °C. The impedance of saline solution and de-ionized water increases sharply at the freezing point, similar to what is known for, e.g., complex tissues, including meat. Yet, only the saline solution impedance shows another sharp increment at a temperature between −30 and −20 °C. Changes of the electric properties after solidification suggest that the latter is linked to transformations of the ice lattice structure. We conclude that the electrical properties might serve as sensitive indicators of these phase changes.

• Bergli, Joakim & Lopez, Alvaro Parra (2020). Synchronization in two-level quantum systems. Physical Review A (PRA). ISSN 2469-9926. 101, s. 062104–062104. doi: 10.1103/PhysRevA.101.062104. Fulltekst i vitenarkiv Vis sammendrag

  Recently, it was shown that dissipative quantum systems with three or more levels are able to synchronize to an external signal. Some researchers have stated that this is not possible for two-level systems, as those systems lack a stable limit cycle in unperturbed dynamics, but others have demonstrated, under a different definition of synchronization, that it is possible in qubits in models which include other elements. We show how a quantum two-level system can be understood as containing a valid limit cycle as the starting point of synchronization and that it can synchronize its dynamics to an external weak signal. This is demonstrated by analytically solving the Lindblad equation of a two-level system coupled to an environment, determining the steady state. This is a mixed state with contributions from many pure states, each of which provides a valid limit cycle. We show that this is sufficient to phase lock the dynamics to a weak external signal, hence clarifying synchronization in two-level systems. We use the Husimi Q representation to analyze the synchronization region, defining a synchronization measure which characterizes the strength of the phase locking. Also, we study the stability of the limit cycle and its deformation with the strength of the signal in terms of the components of the Bloch vector of the system. Finally, we generalize a model of the three-level system to illustrate how the stationary fixed point of that model can be changed into a limit cycle similar to the one that we describe for the two-level system.

• Sørdal, Vegard Børve & Bergli, Joakim (2019). Deep reinforcement learning for quantum Szilard engine optimization. Physical Review A (PRA). ISSN 2469-9926. 100(4). doi: 10.1103/PhysRevA.100.042314. Fulltekst i vitenarkiv Vis sammendrag

  Machine learning techniques based on artificial neural networks have been successfully applied to solve many problems in science. One of the most interesting domains of machine learning, reinforcement learning, has a natural applicability for optimization problems in physics. In this paper, we use deep reinforcement learning and chopped random basis optimization to solve an optimization problem based on the insertion of an off-center barrier in a quantum Szilard engine. We show that by using designed protocols for the time dependence of the barrier strength, we can achieve an equal splitting of the wave function (1/2 probability to find the particle on either side of the barrier) even for an asymmetric Szilard engine in such a way that no information is lost when measuring which side the particle is found. This implies that the asymmetric nonadiabatic Szilard engine can operate with the same efficiency as the traditional Szilard engine with adiabatic insertion of a central barrier. We compare the two optimization methods and demonstrate the advantage of reinforcement learning when it comes to constructing robust and noise-resistant protocols.

• Bergli, Joakim; Adenier, Guillaume; Thörn, Andreas Pierre & Vistnes, Arnt Inge (2019). Frequency and phase relations of entangled photons observed by a two-photon interference experiment. Physical Review A (PRA). ISSN 2469-9926. 100(2), s. 023850-1–023850-11. doi: 10.1103/PhysRevA.100.023850. Fulltekst i vitenarkiv Vis sammendrag

  An entangled photon experiment has been performed with a large variation of the temperature of the nonlinear crystal generating the entangled pair by spontaneous downconversion. The photon pairs are separated by a nonpolarizing beamsplitter, and the polarization modes are mixed by half-wave plates. The correlation function of the coincidences is studied as a function of the temperature. In the presence of a narrow interference filter, we observe that the correlation changes between −1 and +1 about seven times within a temperature interval of about 30∘C. We show that the common simplified single-mode pair representation of entangled photons is insufficient to describe the results, but that the biphoton description that includes frequency and phase details gives a close to perfect fit with experimental data for two different choices of interference filters. We explain the main ideas of the underlying physics, and we give an interpretation of the two-photon amplitude, which provides an intuitive understanding of the effect of changing the temperature and inserting interference filters.

• Sørdal, Vegard Børve & Bergli, Joakim (2019). Quantum particle in a split box: Excitations to the ground state. Physical Review A (PRA). ISSN 2469-9926. 99(2), s. 1–6. doi: 10.1103/PhysRevA.99.022121. Fulltekst i vitenarkiv Vis sammendrag

  We discuss two different approaches for splitting the wave function of a single-particle box (SPB) into two equal parts. Adiabatic insertion of a barrier in the center of a SPB in order to make two compartments which each have probability 1/2 of finding the particle in it is one of the key steps for a Szilard engine. However, any asymmetry between the volume of the compartments due to an off-center insertion of the barrier results in a particle that is fully localized in the larger compartment, in the adiabatic limit. We show that rather than exactly splitting the eigenfunctions in half by a symmetric barrier, one can use a nonadiabatic insertion of an asymmetric barrier to induce excitations to only the first excited state of the full box. As the barrier strength goes to infinity the excited state of the full box becomes the ground state of one of the new boxes. Thus, we can achieve close to exact splitting of the probability between the two compartments using the more realistic nonadiabatic, not perfectly centered barrier, rather than the idealized adiabatic and central barrier normally assumed.

• Sørdal, Vegard Børve; Bergli, Joakim & Galperin, Yuri (2017). Influence of measurement error on Maxwell's demon. Physical Review E (PRE). ISSN 2470-0045. 95(6). doi: 10.1103/PhysRevE.95.062129. Fulltekst i vitenarkiv Vis sammendrag

  In any general cycle of measurement, feedback, and erasure, the measurement will reduce the entropy of the system when information about the state is obtained, while erasure, according to Landauer's principle, is accompanied by a corresponding increase in entropy due to the compression of logical and physical phase space. The total process can in principle be fully reversible. A measurement error reduces the information obtained and the entropy decrease in the system. The erasure still gives the same increase in entropy, and the total process is irreversible. Another consequence of measurement error is that a bad feedback is applied, which further increases the entropy production if the proper protocol adapted to the expected error rate is not applied. We consider the effect of measurement error on a realistic single-electron box Szilard engine, and we find the optimal protocol for the cycle as a function of the desired power P and error ɛ.

• Abie, Sisay Mebre; Bergli, Joakim; Galperin, Yuri & Martinsen, Ørjan Grøttem (2016). Universality of AC conductance in human hair. Biomedical Engineering & Physics Express. 2. doi: 10.1088/2057-1976/2/2/027002. Fulltekst i vitenarkiv
• Sørdal, Vegard Børve; Bergli, Joakim & Galperin, Yuri (2016). Cooling by heating: Restoration of the third law of thermodynamics. Physical Review E (PRE). ISSN 2470-0045. 93(3). doi: 10.1103/PhysRevE.93.032102. Fulltekst i vitenarkiv Vis sammendrag

  We have made a simple and natural modification of a recent quantum refrigerator model presented by Cleuren et al. [Phys. Rev. Lett. 108, 120603 (2012)]. The original model consist of two metal leads acting as heat baths and a set of quantum dots that allow for electron transport between the baths. It was shown to violate the dynamic third law of thermodynamics (the unattainability principle, which states that cooling to absolute zero in finite time is impossible). By taking into consideration the finite energy level spacing Δ, in metals we restore the third law while keeping all of the original model's thermodynamic properties intact down to the limit of kBT∼Δ, where the cooling rate is quenched. The spacing Δ depends on the confinement of the electrons in the lead and therefore, according to our result larger samples (with smaller level spacing), could be cooled efficiently to lower absolute temperatures than smaller ones. However, a large lead makes the assumption of instant equilibration of electrons implausible; in reality one would only cool a small part of the sample and we would have a nonequilibrium situation. This property is expected to be model independent and raises the question whether we can find an optimal size for the lead that is to be cooled. ©2016 American Physical Society

• Pekola, J. P.; Masuyama, Y.; Nakamura, Y.; Bergli, Joakim & Galperin, Yuri (2015). Dephasing and dissipation in qubit thermodynamics. Physical Review E. Statistical, Nonlinear, and Soft Matter Physics. ISSN 1539-3755. 91(6). doi: 10.1103/PhysRevE.91.062109. Fulltekst i vitenarkiv
• Bergli, Joakim (2014). Accuracy of energy measurement and reversible operation of a microcanonical Szilard engine. Physical Review E. Statistical, Nonlinear, and Soft Matter Physics. ISSN 1539-3755. 89(4). doi: 10.1103/PhysRevE.89.042120. Fulltekst i vitenarkiv
• Bergli, Joakim & Galperin, Yuri (2014). Universal scaling form of AC response in variable range hopping. AIP Conference Proceedings. ISSN 0094-243X. 1610, s. 41–41. doi: 10.1063/1.4893508. Fulltekst i vitenarkiv
• Adenier, Guillaume; Bergli, Joakim; Thörn, Andreas Pierre & Vistnes, Arnt Inge (2013). Observation of bosonic coalescence and fermionic anti-coalescence with indistinguishable photons. Proceedings of SPIE, the International Society for Optical Engineering. ISSN 0277-786X. 8832. doi: 10.1117/12.2024090. Fulltekst i vitenarkiv
• Bergli, Joakim; Galperin, Yuri & Kopnin, N. B. (2013). Information flow and optimal protocol for a Maxwell-demon single-electron pump. Physical Review E. Statistical, Nonlinear, and Soft Matter Physics. ISSN 1539-3755. 88(6). doi: 10.1103/PhysRevE.88.062139. Fulltekst i vitenarkiv
• Wold, Henry; Brox, Håkon; Galperin, Yuri & Bergli, Joakim (2012). Decoherence of a qubit due to either a quantum fluctuator, or classical telegraph noise. Physical Review B. Condensed Matter and Materials Physics. ISSN 1098-0121. 86(20). doi: 10.1103/PhysRevB.86.205404. Fulltekst i vitenarkiv
• Brox, Håkon; Bergli, Joakim & Galperin, Yuri (2012). Bloch-sphere approach to correlated noise in coupled qubits. Journal of Physics A: Mathematical and Theoretical. ISSN 1751-8113. 45(45). doi: 10.1088/1751-8113/45/45/455302. Fulltekst i vitenarkiv
• Drichko, IL; Diakonov, AM; Malysh, VA; Smirnov, IY; Koptev, ES & Nikiforov, AI [Vis alle 9 forfattere av denne artikkelen] (2012). Nonlinear high-frequency hopping conduction in two-dimensional arrays of Ge-in-Si quantum dots: Acoustic methods. Solid State Communications. ISSN 0038-1098. 152(10), s. 860–863. doi: 10.1016/j.ssc.2012.02.016. Fulltekst i vitenarkiv
• Bergli, Joakim & Galperin, Yuri (2012). Logarithmic relaxation and stress aging in the electron glass. Physical Review B. Condensed Matter and Materials Physics. ISSN 1098-0121. 85(21). doi: 10.1103/PhysRevB.85.214202. Fulltekst i vitenarkiv
• Brox, Håkon; Bergli, Joakim & Galperin, Yuri (2012). Importance of level statistics in the decoherence of a central spin due to a spin environment. Physical Review A. Atomic, Molecular, and Optical Physics (PRA). ISSN 1050-2947. 85(5). doi: 10.1103/PhysRevA.85.052117. Fulltekst i vitenarkiv
• Bardalen, Eivind; Bergli, Joakim & Galperin, Yuri (2012). Coulomb glasses: A comparison between mean field and Monte Carlo results. Physical Review B. Condensed Matter and Materials Physics. ISSN 1098-0121. 85(15). doi: 10.1103/PhysRevB.85.155206. Fulltekst i vitenarkiv
• Bergli, Joakim; Somoza, A. M. & Ortuno, Miguel (2011). Effects of many-electron jumps in the relaxation and conductivity of Coulomb glasses. Physical Review B. Condensed Matter and Materials Physics. ISSN 1098-0121. 84(17). doi: 10.1103/PhysRevB.84.174201. Fulltekst i vitenarkiv
• Zeng, Hongbo; Kristiansen, Kai; Wang, Peng; Bergli, Joakim & Israelachvili, Jacob (2011). Surface-Induced Patterns from Evaporating Droplets of Aqueous Carbon Nanotube Dispersions. Langmuir. ISSN 0743-7463. 27(11), s. 7163–7167. doi: 10.1021/la200476n. Fulltekst i vitenarkiv
• Brox, Håkon; Bergli, Joakim & Galperin, Yuri (2011). Effects of external driving on the coherence time of a Josephson junction qubit in a bath of two-level fluctuators. Physical Review B. Condensed Matter and Materials Physics. ISSN 1098-0121. 84(24). doi: 10.1103/PhysRevB.84.245416. Fulltekst i vitenarkiv
• Bergli, Joakim; Galperin, Yuri & Altshuler, BL (2009). Decoherence in qubits due to low-frequency noise. New Journal of Physics. 11. doi: 10.1088/1367-2630/11/2/025002. Fulltekst i vitenarkiv
• Kopnin, NB; Galperin, Yuri; Bergli, Joakim & Vinokur, VM (2009). Nonequilibrium electrons in tunnel structures under high-voltage injection. Physical Review B. Condensed Matter and Materials Physics. ISSN 1098-0121. 80(13). doi: 10.1103/PhysRevB.80.134502. Fulltekst i vitenarkiv
• Caravaca, M; Voje, Aurora; Bergli, Joakim; Ortuno, M & Somoza, A (2009). Non-linear conductivity in Coulomb glasses. Annalen der Physik. ISSN 0003-3804. 18(12), s. 873–876. doi: 10.1002/andp.200910377. Fulltekst i vitenarkiv
• Bergli, Joakim; Ortuno, M & Somoza, A (2009). Study of two-electron jumps in relaxation of Coulomb glasses. Annalen der Physik. ISSN 0003-3804. 18(12), s. 877–881. doi: 10.1002/andp.200910376. Fulltekst i vitenarkiv
• Knudsen, Henning Arendt & Bergli, Joakim (2009). Experimental Demonstration of Snell's Law for Shear Zone Refraction in Granular Materials. Physical Review Letters. ISSN 0031-9007. 103(10). doi: 10.1103/PhysRevLett.103.108301. Fulltekst i vitenarkiv
• Kirkengen, Martin & Bergli, Joakim (2009). Slow relaxation and equilibrium dynamics in a two-dimensional Coulomb glass: Demonstration of stretched exponential energy correlations. Physical Review B. Condensed Matter and Materials Physics. ISSN 1098-0121. 79(7). doi: 10.1103/PhysRevB.79.075205. Fulltekst i vitenarkiv
• Vestgården, Jørn Inge; Bergli, Joakim & Galperin, Yuri (2008). Nonlinearly driven Landau-Zener transition in a qubit with telegraph noise. Physical Review B. Condensed Matter and Materials Physics. ISSN 1098-0121. 77. doi: 10.1103/PhysRevB.77.014514. Fulltekst i vitenarkiv
• Glatz, A.; Vinokur, VM; Bergli, Joakim; Kirkengen, Martin & Galperin, Yuri (2008). The Coulomb gap and low energy statistics for Coulomb glasses. Journal of Statistical Mechanics: Theory and Experiment. doi: 10.1088/1742-5468/2008/06/P06006. Fulltekst i vitenarkiv
• Fefelov, Oleg; Bergli, Joakim & Galperin, Yuri (2007). Calculation of the heat capacity of a thin membrane at very low temperature. Physical Review B. Condensed Matter and Materials Physics. ISSN 1098-0121. 75. doi: 10.1103/PhysRevB.75.172101. Fulltekst i vitenarkiv
• Bergli, Joakim & Faoro, L (2007). Exact solution for the dynamical decoupling of a qubit with telegraph noise. Physical Review B. Condensed Matter and Materials Physics. ISSN 1098-0121. 75. doi: 10.1103/PhysRevB.75.054515. Fulltekst i vitenarkiv
• Bergli, Joakim & Glazman, L (2007). Spin echo without an external permanent magnetic field. Physical Review B. Condensed Matter and Materials Physics. ISSN 1098-0121. 76. doi: 10.1103/PhysRevB.76.064301. Fulltekst i vitenarkiv
• Galperin, Yuri; Altshuler, BL; Bergli, Joakim; Shantsev, Daniil & Vinokur, V (2007). Non-Gaussian dephasing in flux qubits due to 1/f noise. Physical Review B. Condensed Matter and Materials Physics. ISSN 1098-0121. 76. doi: 10.1103/PhysRevB.76.064531. Fulltekst i vitenarkiv
• Kirkengen, Martin; Bergli, Joakim & Galperin, Yuri (2007). Direct generation of charge carriers in c-Si solar cells due to embedded nanoparticles. Journal of Applied Physics. ISSN 0021-8979. 102. doi: 10.1063/1.2809368. Fulltekst i vitenarkiv
• Galperin, Yuri; Altshuler, B. L.; Bergli, Joakim & Shantsev, Daniil (2006). Non-Gaussian Low-Frequency Noise as a Source of Qubit Decoherence. Virtual Journal of Applications of Superconductivity. 10(4). Fulltekst i vitenarkiv
• Galperine, Iouri; Altshuler, Boris; Bergli, Joakim & Shantsev, Daniil (2006). Non-Gaussian low-frequency noise as a source of qubit decoherence. Physical Review Letters. ISSN 0031-9007. 96. Fulltekst i vitenarkiv
• Kirkengen, Martin; Bergli, Joakim & Galperin, Yuri (2006). Coherent charge transport through an interface between a superconductor and hopping insulator: Role of barrier properties. Physical Review B. Condensed Matter and Materials Physics. ISSN 1098-0121. 74. Fulltekst i vitenarkiv
• Bergli, Joakim; Galperin, Yuri & Altshuler, Boris (2006). Decoherence of a qubit by non-Gaussian noise at an arbitrary working point. Physical Review B. Condensed Matter and Materials Physics. ISSN 1098-0121. 74. doi: 10.1103/PhysRevB.74.024509. Fulltekst i vitenarkiv
• Galperine, Iouri; Shantsev, Daniil; Bergli, Joakim & Altshuler, Boris (2005). Rabi oscillations of a qubit coupled to a two-level system. Europhysics letters. ISSN 0295-5075. 71, s. 21–27. doi: 10.1209/epl/i2005-10053-y. Fulltekst i vitenarkiv
• Faoro, L.; Bergli, Joakim; Altshuler, Boris & Galperine, Iouri (2005). Models of environment and T-1 relaxation in Josephson charge qubits. Physical Review Letters. ISSN 0031-9007. 95. doi: 10.1103/PhysRevLett.95.046805. Fulltekst i vitenarkiv

Se alle arbeider i NVA

• Bergli, Joakim (2026). Kvantedatamaskiner. Fulltekst i vitenarkiv Vis sammendrag

  Populærforedrag for nye fysikkstudenter

• Pettersen, Markus; Haug, Nicolai; Bergli, Joakim; Surowiec, Thomas & Lepperød, Mikkel (2025). Exponential Maps as an Interpretable Framework for Generating Neural Spatial Representations from First-Principles. Fulltekst i vitenarkiv
• Bergli, Joakim (2025). Quantum syncronization with quantum trajectories. Fulltekst i vitenarkiv Vis sammendrag

  Quantum synchronization is often studied using a master equation, typically the Lindblad equation. This gives the time evolution of the density matrix. If we study the response to a periodic external signal, synchronization is detected by a steady state density matrix that is in phase with the external signal. However, the system will normally only partially synchronize with the degree of synchronization being hard to quantify. This is to some extent similar to the synchronization of a classical system in the presence of external noise, but in that case we can measure the degree of synchronization by the average frequency of the system as compared to the frequency of the external signal. For a quantum system, we apply the quantum trajectory approach, which gives a stochastic trajectory, and measures the average frequency of such trajectories. In this way, we can study the synchronization process in more detail than when using the master equation. We illustrate this by studying the synchronization of a two-level system to an external signal, and the mutual synchronization of two two-level systems.

• Bergli, Joakim (2025). Kvantedatamaskiner og kvantekommunikasjon. Fulltekst i vitenarkiv
• Bergli, Joakim (2024). Decoherence by low frequency noise and exceptional points of non-Hermitian matrices. Fulltekst i vitenarkiv Vis sammendrag

  Decoherence is the main obstacle to constructing reliable quantum computers. Therefore, it is important to understand the physical mechanisms of decoherence. In superconducting quantum devices, it is observed that the noise spectrum of the environment often is dominated by low frequencies, the so-called 1/f noise. I will describe how we can model 1/f noise by random telegraph processes. In this context, there appears a sudden change in behavior as the parameters of the model are changed, which can be understood in terms of an exceptional point of a non-Hermitian matrix. I will explain what this means and how this concept can appear in other contexts.

• Bergli, Joakim (2024). Quantum Computers: Why would we like to build one and how can we do it? Fulltekst i vitenarkiv
• Bergli, Joakim (2020). Kvantedatamaskiner Hvorfor vil vi bygge dem, og hvordan kan det gjøres? Fulltekst i vitenarkiv
• Bergli, Joakim (2019). Pure phase decoherence in a ring:a geometric approach. Fulltekst i vitenarkiv
• Galperin, Yuri; Bergli, Joakim & Sørdal, Vegard Børve (2018). Optimal protocols for a Maxwell Demon device with errors. Fulltekst i vitenarkiv
• Martinsen, Ørjan Grøttem; Abie, Sisay Mebre; Bergli, Joakim & Galperin, Yuri (2016). Universality of low frequency conductance of human hair. Proceedings of the 16th International Conference on Electrical Bioimpedance. s. 91–91. Fulltekst i vitenarkiv
• Bergli, Joakim; Galperin, Yuri; Martinsen, Ørjan Grøttem & Abie, Sisay Mebre (2016). Universality of AC conductance in human hair. Fulltekst i vitenarkiv
• Pekola, J. P.; Masuyama, Y.; Nakamura, Y.; Bergli, Joakim & Galperin, Yuri (2015). Dephasing and Dissipation in Qubit Thermodynamics. Fulltekst i vitenarkiv
• Pekola, J. P.; Masuyama, Y.; Nakamura, Y.; Bergli, Joakim & Galperin, Yuri (2015). Dephasing and dissipation in qubit thermodynamics. Fulltekst i vitenarkiv
• Martinsen, Ørjan Grøttem; Grimnes, Sverre; Bergli, Joakim & Galperin, Yuri (2013). Universality in the electrical conductance of human hair. Fulltekst i vitenarkiv
• Bergli, Joakim & Galperin, Yuri (2013). Universal scaling form of AC response in variable range hopping. Fulltekst i vitenarkiv
• Bergli, Joakim (2011). Relaxation processes in Coulombglasses. Fulltekst i vitenarkiv
• Bergli, Joakim (2011). Maxwell's demon and the second lawof thermodynamics. Fulltekst i vitenarkiv
• Bergli, Joakim (2010). Hot Electrons. Fulltekst i vitenarkiv
• Bergli, Joakim (2010). Slow Relaxation and Equilibrium. Dynamics in a 2 D Coulomb Glass: Demonstration of Stretched Exponential. Energy Correlations. Fulltekst i vitenarkiv
• Bergli, Joakim (2009). Study of two-electron jumps in relaxation of Coulomb glasses. Fulltekst i vitenarkiv
• Bergli, Joakim (2009). Study of two-electron jumps in relaxation of Coulomb glasses. Fulltekst i vitenarkiv
• Bergli, Joakim (2009). Slow Relaxation and Equilibrium Dynamics in a 2 D Coulomb Glass: Demonstration of Stretched Exponential Energy Correlations. Fulltekst i vitenarkiv
• Bergli, Joakim (2009). Snell’s law for shear zonerefraction in granular materials. Fulltekst i vitenarkiv
• Bergli, Joakim (2009). Slow Relaxation and Equilibrium Dynamics in a 2 D Coulomb Glass: Demonstration of Stretched Exponential Energy Correlations. Fulltekst i vitenarkiv
• Bergli, Joakim (2009). Kvantedatamaskiner. Fulltekst i vitenarkiv
• Galperin, Yuri; Bergli, Joakim & Altshuler, Boris (2008). Decoherence in quantum devices due to low-frequency noise of environment: Role of non-Gaussian effects. Fulltekst i vitenarkiv
• Bergli, Joakim (2007). Exact solution for the dynamical decoupling of a qubit with telegraph noise. Fulltekst i vitenarkiv
• Kirkengen, Martin; Bergli, Joakim & Galperin, Yuri (2007). Surface Plasmons in Solar Cells. Fulltekst i vitenarkiv
• Bergli, Joakim (2007). Maxwells demon. [Radio]. Verdt å vite, NRK p2. Fulltekst i vitenarkiv
• Bergli, Joakim (2007). Kvantedatamaskiner - hvorfor vil vi bygge en, og hverdan kan det gjøres? Fulltekst i vitenarkiv
• Bergli, Joakim (2007). Om jordas magnetfelt. [Radio]. Verdt å vite. Fulltekst i vitenarkiv
• Bergli, Joakim (2006). Spin echo in an arbitrary magnetic field: How to undo an unknown rotation. Fulltekst i vitenarkiv
• Bergli, Joakim (2006). `Spin echo in an arbitrary magnetic field: How to undo an unknown rotation. Fulltekst i vitenarkiv
• Bergli, Joakim (2006). Dynamical decoupling of a qubit with telegraph noise. Fulltekst i vitenarkiv
• Bergli, Joakim (2006). Spin echo in an arbitrary magnetic field: How to undo an unknown rotation. Fulltekst i vitenarkiv
• Bergli, Joakim (2006). Solving quantum problems on a quantum computer. Fulltekst i vitenarkiv
• Bergli, Joakim (2006). Spin echo in an arbitrary magnetic field: How to undo an unknown rotation. Fulltekst i vitenarkiv
• Galperin, Yuri; Shantsev, Daniil; Bergli, Joakim & Altshuler, B. L. (2006). Rabi oscillations of a qubit coupled to a two-level system. Fulltekst i vitenarkiv
• Galperin, Yuri; Bergli, Joakim; Altshuler, B. L.; Shantsev, Daniil; Faoro, L. & Martin, I (2006). Non-Gaussian Low-Frequency Noise as a Source of Qubit Decoherence. Fulltekst i vitenarkiv
• Bergli, Joakim (2005). Models of environment and T1 relaxation of superconducting qubits. Fulltekst i vitenarkiv
• Bergli, Joakim (2005). Models of environment and T1 relaxation in Superconducting qubits. Fulltekst i vitenarkiv
• Bergli, Joakim (2005). Models of environment and T1 relaxation of superconducting qubits. Fulltekst i vitenarkiv
• Bergli, Joakim (2005). Quantum Computing. Fulltekst i vitenarkiv
• Bergli, Joakim (2005). Hvorfor har jorda et magnetfelt? Fulltekst i vitenarkiv
• Shantsev, Daniil; Galperin, Yuri; Altshuler, B. L. & Bergli, Joakim (2005). Non-Gaussian low-frequency noise as a source of qubit decoherence. Fulltekst i vitenarkiv
• Musland, Lars; Flage-Larsen, Espen; Prytz, Øystein & Bergli, Joakim (2019). Theory and calculations of thermoelectric transport in heterostructures. Universitetet i Oslo. Fulltekst i vitenarkiv

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