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Search Results: 1 - 10 of 15 matches for " Tauno Palomaki "
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The Single-Photon Router
Io-Chun Hoi,C. M. Wilson,G?ran Johansson,Tauno Palomaki,Borja Peropadre,Per Delsing
Physics , 2011, DOI: 10.1103/PhysRevLett.107.073601
Abstract: We have embedded an artificial atom, a superconducting "transmon" qubit, in an open transmission line and investigated the strong scattering of incident microwave photons ($\sim6$ GHz). When an input coherent state, with an average photon number $N\ll1$ is on resonance with the artificial atom, we observe extinction of up to 90% in the forward propagating field. We use two-tone spectroscopy to study scattering from excited states and we observe electromagnetically induced transparency (EIT). We then use EIT to make a single-photon router, where we can control to what output port an incoming signal is delivered. The maximum on-off ratio is around 90% with a rise and fall time on the order of nanoseconds, consistent with theoretical expectations. The router can easily be extended to have multiple output ports and it can be viewed as a rudimentary quantum node, an important step towards building quantum information networks.
Giant Cross Kerr Effect for Propagating Microwaves Induced by an Artificial Atom
Io-Chun Hoi,C. M. Wilson,G?ran Johansson,Tauno Palomaki,Thomas M. Stace,Bixuan Fan,Per Delsing
Physics , 2012, DOI: 10.1103/PhysRevLett.111.053601
Abstract: We have investigated the cross Kerr phase shift of propagating microwave fields strongly coupled to an artificial atom. The artificial atom is a superconducting transmon qubit in an open transmission line. We demonstrate average phase shifts of 11 degrees per photon between two coherent microwave fields both at the single-photon level. At high control power, we observe phase shifts up to 30 degrees. Our results provide an important step towards quantum gates with propagating photons in the microwave regime.
Microwave Quantum Optics with an Artificial Atom
Io-Chun Hoi,C. M. Wilson,G?ran Johansson,Joel Lindkvist,Borja Peropadre,Tauno Palomaki,Per Delsing
Physics , 2012, DOI: 10.1088/1367-2630/15/2/025011
Abstract: We address the recent advances on microwave quantum optics with artificial atoms. This field relies on the fact that the coupling between a superconducting artificial atom and propagating microwave photons in a 1D open transmission line can be made strong enough to observe quantum coherent effects, without using any cavity to confine the microwave photons. We investigate the scattering properties in such a system with resonant coherent microwaves. We observe the strong nonlinearity of the artificial atom and under strong driving we observe the Mollow triplet. By applying two resonant tones, we also observe the Autler-Townes splitting. By exploiting these effects, we demonstrate two quantum devices at the single-photon level in the microwave regime: the single-photon router and the photon-number filter. These devices provide essential steps towards the realization of an on-chip quantum network.
BUT WHO LEARNS WHAT ? ON THE RISKS OF KNOWLEDGE ACCUMULATION THROUGH NETWORKED LEARNING IN R&D
TAUNO KEK?LE,SARA CERVAI,ANA GOMEZ BERNABEU
Quality Innovation Prosperity , 2009,
Abstract: In big companies, managerial activities and organizational boundaries will over time hide most unevenly developed skill and knowledge distribution patterns; studying the organizations with the means of modern applied physics is thus quite difficult. People are forced to communicate along the organizational lines, and their personal preferences that could affect the communication networks are often dampened to nearly obsolete. In small companies, however, as well as other less structured non-business organizations, many network patterns exist, based on the preferred cooperation and communication behaviour of human beings, and are observable in various real-life situations. Given their free choice of either to solve the problem themselves or go to one of the colleagues to ask for help, and a preference based on the transactive memory of the organization (a word-of-mouth "reputation" information about who has the skill needed to solve the problem, or who solved the previous one with some similarity) will over time lead to most difficult problems always being solved by one or two key individuals. This paper tests this idea with an agent model to confirm the accumulation of critical knowledge to few individuals. Furthermore, the paper presents a network relation study in a 45-person software solution company. It seems the knowledge is on its way to become distributed according to power law – centralized more and more to a couple of individuals – also in the reality of this case company, even if there are not enough interactions in the five-year history of the company to prove this in a statistically significant way.
Nanosecond laser treatment of graphene
Valter Kiisk,Tauno Kahro,Jekaterina Kozlova,Leonard Matisen,Harry Alles
Physics , 2013, DOI: 10.1016/j.apsusc.2013.03.047
Abstract: Laser processing of graphene is of great interest for cutting, patterning and structural engineering purposes. Tunable nanosecond lasers have the advantage of being relatively widespread (compared to e.g. femtosecond or high-power continuous wave lasers). Hereby we have conducted an investigation of the impact of nanosecond laser pulses on CVD graphene. The damage produced by sufficiently strong single shots (pulse width 5 ns, wavelength 532 or 266 nm) from tunable optical parametric oscillator was investigated by the methods of scanning electron microscopy and optical microspectroscopy (Raman and fluorescence). Threshold of energy density for producing visible damage was found to be ~200 mJ/cm2. For UV irradiation the threshold could be notably less depending on the origin of sample. Surprisingly strong fluorescence signal was recorded from damaged areas and is attributed to the residues of oxidized graphene.
State Transfer Between a Mechanical Oscillator and Microwave Fields in the Quantum Regime
T. A. Palomaki,J. W. Harlow,J. D. Teufel,R. W. Simmonds,K. W. Lehnert
Physics , 2012, DOI: 10.1038/nature11915
Abstract: Recently, macroscopic mechanical oscillators have been coaxed into a regime of quantum behavior, by direct refrigeration [1] or a combination of refrigeration and laser-like cooling [2, 3]. This exciting result has encouraged notions that mechanical oscillators may perform useful functions in the processing of quantum information with superconducting circuits [1, 4-7], either by serving as a quantum memory for the ephemeral state of a microwave field or by providing a quantum interface between otherwise incompatible systems [8, 9]. As yet, the transfer of an itinerant state or propagating mode of a microwave field to and from a mechanical oscillator has not been demonstrated owing to the inability to agilely turn on and off the interaction between microwave electricity and mechanical motion. Here we demonstrate that the state of an itinerant microwave field can be coherently transferred into, stored in, and retrieved from a mechanical oscillator with amplitudes at the single quanta level. Crucially, the time to capture and to retrieve the microwave state is shorter than the quantum state lifetime of the mechanical oscillator. In this quantum regime, the mechanical oscillator can both store and transduce quantum information.
Temperature induced inversion of oxygen response in CVD graphene on SiO2
Raivo Jaaniso,Tauno Kahro,Jekaterina Kozlova,Jaan Aarik,Lauri Aarik,Harry Alles,Aare Floren,Alar Gerst,Aarne Kasikov,Ahti Niilisk,V?ino Sammelselg
Physics , 2013, DOI: 10.1016/j.snb.2013.09.068
Abstract: We have synthesized single-layer graphene on Cu foils using chemical vapor deposition method and transferred the graphene to the top of a Si/SiO2 substrate with a pair of prefabricated Ti/Au electrodes. A resistive graphene-based gas sensor prepared in this way revealed n-type oxygen response at room temperature and we have successfully fitted the data obtained with varying oxygen levels using a two-site Langmuir model. P-type oxygen response of our sensor was observed after the temperature was raised to 100 oC, with a reversible transition to n-type behaviour when the temperature was lowered back to room temperature. Such inversion of the gas response type with temperature was interpreted as a result of interplay between the adsorbate-induced charge transfer and charge carrier scattering. The transduction function was derived, which relates the electrical response to surface coverage through both the induced mobility and charge density changes.
Distinct differentiation characteristics of individual human embryonic stem cell lines
Milla Mikkola, Cia Olsson, Jaan Palgi, Jarkko Ustinov, Tiina Palomaki, Nina Horelli-Kuitunen, Sakari Knuutila, Karolina Lundin, Timo Otonkoski, Timo Tuuri
BMC Developmental Biology , 2006, DOI: 10.1186/1471-213x-6-40
Abstract: The cell lines were cultured either on human or mouse feeder cells. The cells grew significantly faster and could be passaged enzymatically only on mouse feeders. However, this was found to lead to chromosomal instability after prolonged culture. All hESC lines expressed the established markers of pluripotent cells as well as several primordial germ cell (PGC) marker genes in a uniform manner. However, the cell lines showed distinct features in their spontaneous differentiation patterns. The embryoid body (EB) formation frequency of FES 30 cell line was significantly lower than that of other lines and cells within the EBs differentiated less readily. Likewise, teratomas derived from FES 30 cells were constantly cystic and showed only minor solid tissue formation with a monotonous differentiation pattern as compared with the other lines.hESC lines may differ substantially in their differentiation properties although they appear similar in the undifferentiated state.Embryonic stem (ES) cells are pluripotent cells derived from the inner cell mass (ICM) of the mammalian blastocyst. They have the potential to differentiate, both in vitro and in vivo, into derivatives of all three embryonic germ cell layers. According to current understanding, ES cells can be maintained in an undifferentiated stage indefinitely in adequate culture conditions [1].The first human ES cell (hESC) lines were isolated in 1998 raising hopes for hESC derived cell replacement therapies for various degenerative diseases [2]. As the ES cell lines are derived from individual embryos, they are likely to have unique characteristics. Recent studies focusing on epigenetic of different hESC lines have indeed indicated that individual cell lines may have distinct line specific epigenetic profiles [3,4] which may affect their differentiation properties. Adaptation to distinct cell culture conditions may cause selection pressure altering the features of the cell lines at the epigenetic or chromosomal level.
Decoherence in dc SQUID phase qubits
Hanhee Paik,S. K. Dutta,R. M. Lewis,T. A. Palomaki,B. K. Cooper,R. C. Ramos,H. Xu,A. J. Dragt,J. R. Anderson,C. J. Lobb,F. C. Wellstood
Physics , 2008, DOI: 10.1103/PhysRevB.77.214510
Abstract: We report measurements of Rabi oscillations and spectroscopic coherence times in an Al/AlOx/Al and three Nb/AlOx/Nb dc SQUID phase qubits. One junction of the SQUID acts as a phase qubit and the other junction acts as a current-controlled nonlinear isolating inductor, allowing us to change the coupling to the current bias leads in situ by an order of magnitude. We found that for the Al qubit a spectroscopic coherence time T2* varied from 3 to 7 ns and the decay envelope of Rabi oscillations had a time constant T' = 25 ns on average at 80 mK. The three Nb devices also showed T2* in the range of 4 to 6 ns, but T' was 9 to 15 ns, just about 1/2 the value we found in the Al device. For all the devices, the time constants were roughly independent of the isolation from the bias lines, implying that noise and dissipation from the bias leads were not the principal sources of dephasing and inhomogeneous broadening.
Comparison of coherence times in three dc SQUID phase qubits
Hanhee Paik,B. K. Cooper,S. K. Dutta,R. M. Lewis,R. C. Ramos,T. A. Palomaki,A. J. Przybysz,A. J. Dragt,J. R. Anderson,C. J. Lobb,F. C. Wellstood
Physics , 2007, DOI: 10.1109/TASC.2007.898124
Abstract: We report measurements of spectroscopic linewidth and Rabi oscillations in three thin-film dc SQUID phase qubits. One device had a single-turn Al loop, the second had a 6-turn Nb loop, and the third was a first order gradiometer formed from 6-turn wound and counter-wound Nb coils to provide isolation from spatially uniform flux noise. In the 6 - 7.2 GHz range, the spectroscopic coherence times for the gradiometer varied from 4 ns to 8 ns, about the same as for the other devices (4 to 10 ns). The time constant for decay of Rabi oscillations was significantly longer in the single-turn Al device (20 to 30 ns) than either of the Nb devices (10 to 15 ns). These results imply that spatially uniform flux noise is not the main source of decoherence or inhomogenous broadening in these devices.
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