CoE in Low Temperature Quantum Phenomena and Devices

Coordinator: Prof. Mikko Paalanen, Low Temperature Laboratory, TKK

Vice-coordinator: Research Prof. Heikki Seppä, Quantronics group, VTT

Scientific Advisory Board (SAB):

Professor William Halperin, Northwestern University, Evanston, Illinois, USA (2009-2011)

Professor Mats Jonson, University of Gothenburg, Gothenburg, Sweden and Heriot-Watt University, Edinburgh, Scotland (2006-2011)

Professor John Saunders, Royal Holloway, University College London, UK (2006-2008)



At low temperatures, physical systems eventually condense into their quantum mechanical ground state, and may exhibit extraordinary properties. Known examples are, for example, the superconducting state of metals, in which the electric current flows lossless, and the superfluid state of helium, in which the flow is lossless. Both are examples of macroscopic quantum-mechanical phenomena that occur at low temperatures. The Centre of Excellence on Low Temperature Quantum Phenomena and Devices investigates quantum phenomena, both in extremely ideal continuous media, such as helium liquids and crystals, and in metallic nanostructures. The goal is to produce quantum electronic components with sensors based on superconducting structures as the important circuit elements. A successful example is the superconducting sensors used to measure brain activity.

Research groups

The CoE comprises seven research groups, six from Low Temperature Laboratory of Helsinki University of Technology and Quantronics group from the Microtechnologies and Electronics Unit of VTT. About 25 PhD-level researchers work in the CoE.


Group leader: Prof. Matti Krusius

Contact information: Currently not present at LTL.

ROTA publications


Group leader: Doc. Juha Tuoriniemi

Tel: +358 50 344 2846
Email: Email
Office: 178b (Puumiehenkuja 2B)
Postal address: O.V. Lounasmaa Laboratory, Aalto University School of Science,
P.O. Box 15100, FI-00076 AALTO, Finland

µKI publications


Group leader: Prof. Pertti Hakonen

Tel: +358 50 344 2316
Email: Email
Office: 175a (Puumiehenkuja 2B)
Postal address: O.V. Lounasmaa Laboratory, Aalto University School of Science,
P.O. Box 15100, FI-00076 AALTO, Finland

NANO publications


Group leader: Prof. Jukka Pekola

Tel: +358 50 344 2697
Email: Email
Office: 4110 (Micronova, Tietotie 3)
Postal address: O.V. Lounasmaa Laboratory, Aalto University School of Science,
P.O. Box 13500, FI-00076 AALTO, Finland

PICO publications


Group leader: Dr. Sorin Paraoanu

Tel: +358 50 344 2650
Email: Email
Office: 176a (Puumiehenkuja 2B)
Postal address: O.V. Lounasmaa Laboratory, Aalto University School of Science,
P.O. Box 15100, FI-00076 AALTO, Finland

KVANTTI Publications


Group leader: Doc. Tero Heikkilä

Contact information: Currently not present at LTL.

THEORY publications


Group leader: Docent Panu Helistö

Tel: +20-722-6827


Office: Micronova

Postal address: VTT, P.O. Box 1000, 02044 VTT, Finland

QUANTRONICS publications

Awards and honors

In 2009 Mika Sillanpää from LTL was elected to the Academy Club for Young Scientists by the Finnish Academy of Science and Letters. Tero Heikkilä and Mika Sillanpää from LTL have received the ERC Starting Grant 2009. With the help of this presitigious new European grant Heikkilä will study for next five years Mesoscopic heattronics: thermal and nonequilibrium effects and fluctuations in nanoelectronics. Sillanpää will study Electromechanical coherent quantum systems.

In 2008 Mikko Paalanen received the Theodor Homén Prize in Physics from the Finnish Society of Sciences and Letters. Rob Blaauwgeers and Pieter Vorselman won the 3rd Prize in national Venture Cup competition with their business plan Bluefors Cryogenics.

In 2007 Matti Krusius was awarded an honorary doctorate in Physics in Lancaster University and Grigory Volovik was elected to Leopoldina, the German National Academy of Sciences.

In 2006 The Royal Society of Arts and Sciences in Göteborg elected Mikko Paalanen to be a foreign member of its physics group. The Royal Society in Gothenburg, founded in 1778, is one of the oldest scientific societies in the world.

Research highlights


Superconductivity in lithium below 0.4 millikelvin at ambient pressure
Tuoriniemi J., Juntunen-Nurmilaukas K., Uusvuori J., Pentti E., Salmela A., and Sebedash A.
NATURE 447,187-189 (2007).
Elements in the alkali metal series are regarded as unlikely superconductors because of their monovalent character. A superconducting transition temperature as high as 20 K, recently found in compressed lithium (the lightest alkali element), probably arises from pressure-induced changes in the conduction-electron band structure. Superconductivity at ambient pressure in lithium has hitherto remained unresolved, both theoretically and experimentally. Here we demonstrate that lithium is a superconductor at ambient pressure with a transition temperature of 0.4 mK. As lithium has a particularly simple conduction electron system, it represents an important case for any attempts to classify superconductors and transition temperatures, especially to determine if any non-magnetic configuration can exclude superconductivity down to zero temperature. Furthermore, the combination of extremely weak superconductivity and relatively strong nuclear magnetism in lithium would clearly lead to mutual competition between these two ordering phenomena under suitably prepared conditions.

Hybrid single-electron transistor as a source of quantized electric current Pekola J.R., Vartiainen J.J., Mottonen M., Saira O.P., Meschke M., and Averin D.V.
NATURE PHYSICS 4,120-124 (2008)
The basis of synchronous manipulation of individual electrons in solid-state devices was laid by the rise of single electronics about two decades ago. Ultrasmall structures in a low-temperature environment form an ideal domain for addressing electrons one by one. In the so-called metrological triangle, voltage from the Josephson effect and resistance from the quantum Hall effect would be tested against current via Ohm's law for a consistency check of the fundamental constants of nature, h and e. Several attempts to create a metrological current source that would comply with the demanding criteria of extreme accuracy, high yield and implementation with not too many control parameters have been reported. Here, we propose and prove the unexpected concept of a hybrid normal-metal-superconductor turnstile in the form of a one-island single-electron transistor with one gate, which demonstrates robust current plateaux at multiple levels of ef at frequency f.

THz imaging
VTT Quantronics Group
VTT has developed a THz imaging system (1) based on superconducting transition detectors and patented (2) readout electronics which utilizes eletrothermal feedback in a novel way. The imaging system has produced state-of-the-art THz images and videos and it will be soon be deployed at Helsinki-Vantaa airport for field testing.

1. Luukanen A, Helistö P., Lappalainen P., Leivo M., Rautiainen A, Toivanen H., Seppä H., Taylor Z., Dietlein C.R., and Grossman E.N., Stand-off passive THz imaging at 8-meter stand-off distance: Results from a 64-channel real-time imager [doi-link: 10.1117/12.821996]; Passive Millimeter-Wave Imaging Technology XII, Orlando, FL, USA, 16 April 2009; Proceedings of SPIE - The International Society for Optical Engineering 7309, 73090F, (2009).

2. Seppä H., and Helistö P., Coupling and method for a transition-edge bolometer, Pat. WO2006120290 A1, publication date 16 Nov. 2006, application number WO2006FI152A, application date 10 May 2006, priority FI2005515A (2006).


Nuclear Spin Ordering on the Surface of a He-3 Crystal: Magnetic Steps
Todoshchenko, I.A., Alles H., Junes H.J., Manninen M.S., and Parshin A.Y.
PHYSICAL REVIEW LETTERS 102, 245302 (2009).
The growth rates of the (110) and (100) facets on bcc He-3 crystals have been measured near the magnetic ordering transition at T-N=0.93 mK. In the ordered phase, we have observed several growth modes which correspond to different values of the step energy. We show that, because of quantum delocalization, the step induces a cluster of ferromagnetically ordered nuclear spins. The free energy of such a cluster is relatively large and depends on the orientation of the underlying antiferromagnetic domain. In the paramagnetic phase, the mobilities of the basic facets are greatly reduced because of the much slower spin diffusion in the bulk solid.

Pushing mechanical oscillators towards the quantum limit
Hakonen P.J., and Sillanpää M.A., CONDENSED-MATTER PHYSICS Coupled vibrations
NATURE 459,923-924 (2009).
Demonstrating that macroscopic objects can display quantum behaviour, which is usually associated with the microscopic world of atoms, is a long-standing goal in physics. That goal is now within closer reach.
Sillanpaa M.A., Sarkar J., Sulkko J., Muhonen J., and Hakonen P.J.

Strong Gate Coupling of High-Q Nanomechanical Resonators
Jaakko Sulkko, Mika A. Sillanpää, Pasi Häkkinen, Lorenz Lechner, Meri Helle, Andrew Fefferman, Jeevak Parpia, and Pertti J. Hakonen
NANO LETTERS 10, 4884–4889 (2010).
The detection of mechanical vibrations near the quantum limit is a formidable challenge since the displacement becomes vanishingly small when the number of phonon quanta tends toward zero. An interesting setup for on-chip nanomechanical resonators is that of coupling them to electrical microwave cavities for detection and manipulation. We have shown how to achieve a large cavity coupling energy of up to (2π) 1 MHz/nm for metallic beam resonators at tens of megahertz. We used focused ion beam (FIB) cutting to produce uniform slits down to 10 nm, separating patterned resonators from their gate electrodes, in suspended aluminum films. We measured the thermomechanical vibrations down to a temperature of 25 mK, and we obtained a low number of about 20 phonons at the equilibrium bath temperature. The mechanical properties of Al were excellent after FIB cutting, and we recorded a quality factor of Q ∼ 3 × 105 for a 67 MHz resonator at a temperature of 25 mK.

Electronic Refrigeration at the Quantum Limit
Timofeev A.V., Helle M., Meschke M., Mottonen M., and Pekola J.P.
PHYSICAL REVIEW LETTERS 102, 200801 (2009).
We demonstrate quantum-limited electronic refrigeration of a metallic island in a low-temperature microcircuit. We show that matching the impedance of the circuit enables refrigeration at a distance, of about 50 mu m in our case, through superconducting leads with a cooling power determined by the quantum of thermal conductance. In a reference sample with a mismatched circuit this effect is absent. Our results are consistent with the concept of electromagnetic heat transport. We observe and analyze the crossover between electromagnetic and quasiparticle heat flux in a superconductor.

Societal impact


European and Finnish databases contain information on 39 pending or granted patents, filed by the CoE scientists, and made public in 2006-2010.

Spinoff companies

Since 2006 the scientists of the CoE have founded one spinoff company, Bluefors Cryogenics in 2008. Bluefors is manufactoring dry pulse-tube-driven dilution refrigerators. The CoE is closely collaborating with its older spinoff companies, Nanoway Cryoelectronics, founded in 2003, and Aivon Oy, founded in 2005.



  1. Fan Wu 2007, Supervisor Pertti Hakonen, (postdoc, Chalmers University of Technology, Sweden)
  2. Teemu Ojanen 2007, Supervisor Tero Heikkilä, Opponent Frank Wilhelm (postdoc, Free University of Berlin, Germany) (PDF)
  3. Heikki Junes 2009, Supervisor Harry Alles, Opponent Reyer Jochemsen (business developer, Instrum Justitia Oy) (PDF)
  4. Elias Pentti 2009, Supervisor Juha Tuoriniemi, Opponent Brian Cowan (project leader, Pöyry Environment Oy) (PDF)
  5. Andrey Timofeev 2009, Supervisor Jukka Pekola, Opponent Klaus Ensslin (researcher, VTT, State Research Center) (PDF)
  6. Antti Kemppinen 2009, Supervisor Jukka Pekola, Opponent Per Delsing (researcher, Center for Metrology and Accreditation) (PDF)
  7. Pauli Virtanen 2009, Supervisor Tero Heikkilä, Opponent Carlo Beenakker (postdoc, University of Würsburg, Germany) (PDF)
  8. Tommy Holmqvist 2010, Supervisor Jukka Pekola, Opponent Fransesco Giazotto (Micronova Nanofab, NRI Coordinator) (PDF)
  9. Robert Jan de Graaf 2011, Supervisors Matti Krusius and Vladimir Eltsov, Opponent Shaun Fisher.


  1. Anssi Salmela 2006, Supervisor Juha Tuoriniemi (graduate student, LTL)
  2. Tomi Ruokola 2006, Supervisor Juha Kopu (graduate student, Department of Applied Physics)
  3. Juha Voutilainen 2007, Supervisor Tero Heikkilä (graduate student, LTL)
  4. Olli-Pentti Saira 2007, Supervisor Jukka Pekola (graduate student, LTL)
  5. Antti Paila 2007, Supervisor Pertti Hakonen (graduate student, LTL)
  6. Juho Rysti 2007, Supervisor Juha Tuoriniemi (graduate student, LTL)
  7. Joonas Peltonen 2008, Supervisor Jukka Pekola (graduate student, LTL)
  8. Matti Manninen 2008, Supervisor Harry Alles (graduate student, LTL)
  9. Jaakko Hosio 2008, Supervisor Matti Krusius (graduate student, LTL)
  10. Matti Laakso 2008, Supervisor Tero Heikkilä (graduate student, LTL)
  11. Juha Muhonen 2008, Supervisor Jukka Pekola (graduate student, LTL)
  12. Laura Korhonen 2009, Supervisor Pertti Hakonen (graduate student, Department of Applied Physics)
  13. Pasi Lähteenmäki 2010, Supervisor Pertti Hakonen (graduate student, LTL)
  14. Antti Puska 2010, Supervisor Pertti Hakonen (graduate student, LTL)
  15. Heikkinen Petri 2010, Supervisor Matti Krusius (graduate student, LTL)

Non-public information on the intranet