Pictures of ion crystals with varying number of ion qubits - each bright blob is a single trapped ion.
Trapped-ion quantum computer
Trapped ions are a leading technology for realising a quantum computer. Here ions are confined in a linear Paul trap and are cooled by laser light. The ions repel each other due to Coulomb interaction and crystallize in linear, 2d, or 3d structures depending on the number of ions and the shape of the confining potential (see pictures of ion crystals above). Thanks to ultra-high vacuum conditions and the deep confining potential, the ions are well isolated from the environment and stay trapped for days. Quantum information is encoded in the ions’ electronic states and is manipulated by laser or microwave pulses. Also, the ions in the trap can exchange quantum information via their common motion or Rydberg interaction, which makes it possible to perform quantum calculations on an ion string.
There are several advantages of trapped ion quantum computers over solid-state technologies like superconducting systems
Ions are made by nature. There is no variation in properties due to imprecise manufacturing processes.
Each ion can encode one qubit. In principle, trapping more ions means more qubits.
The quantum state of ion qubits is manipulated by laser light and read out by fluorescence detection. There is no need for complicated wiring.
Ion trap quantum computers are operated at room temperature. Microkelvin temperatures are achieved by laser cooling not by technically demanding cryogenics.
The trapped ion approach has set several highest level benchmarks for quantum computation, in particular
Qubit storage times can reach minutes or even hours [1].
The record for lowest error two-qubit operations (<10^{-3}) is held by trapped ion systems [2, 3].
Multi-qubit operations can generate large entangled states with up to 20 ions [4, 5].
Quantum simulations have been performed with up to 53 ion qubits [6].
Fluorescence detection can determine the quantum state with an error <10^{-3} [7].
Trapped ions also have a leading role in the implementation of quantum algorithms [8, 9, 10] and quantum error correction [11, 12, 13]. As an example, trapped ions have been used in the first realization of an uncompiled, scalable version of Shor’s factorization algorithm [10].
Video: Quantum jumps of trapped ion qubits.
Our research
We are the only group working on trapped ion quantum computers in Sweden. We are developing techniques for fast and precise quantum calculations on large number of trapped ion qubits. Recently we have realised a sub-microsecond quantum gate operation on two trapped ion qubits [14]. By using larger ion crystals with more qubits we plan to further speed up these quantum gates by more than a factor of 10.
References
Single-qubit quantum memory exceeding ten-minute coherence time
Ye Wang, Mark Um, Junhua Zhang, Shuoming An, Ming Lyu, Jing -Ning Zhang, L.-M. Duan, Dahyun Yum, Kihwan Kim Nature Photonics 11, 646–650 (2017).
High-Fidelity Quantum Logic Gates Using Trapped-Ion Hyperfine Qubits
C. J. Ballance, T. P. Harty, N. M. Linke, M. A. Sepiol, and D. M. Lucas Phys. Rev. Lett. 117, 060504 (2016).
High-Fidelity Universal Gate Set for ^{9}Be^{+} Ion Qubits
J. P. Gaebler, T. R. Tan, Y. Lin, Y. Wan, R. Bowler, A. C. Keith, S. Glancy, K. Coakley, E. Knill, D. Leibfried, D. J. Wineland Phys. Rev. Lett. 117, 060505 (2016).
Observation of Entangled States of a Fully Controlled 20-Qubit System
Nicolai Friis, Oliver Marty, Christine Maier, Cornelius Hempel, Milan Holzäpfel, Petar Jurcevic, Martin B. Plenio, Marcus Huber, Christian Roos, Rainer Blatt, Ben Lanyon Phys. Rev. X 8, 021012 (2018).
14-qubit entanglement: creation and coherence
T. Monz, P. Schindler, J.T. Barreiro, M. Chwalla, D. Nigg, W.A. Coish, M. Harlander, W. Hänsel, M. Hennrich, and R. Blatt Physical Review Letters 106, 130506 (2011).
Observation of a many-body dynamical phase transition with a 53-qubit quantum simulator
J. Zhang, G. Pagano, P. W. Hess, A. Kyprianidis, P. Becker, H. Kaplan, A. V. Gorshkov, Z.-X. Gong, C. Monroe Nature 551, 601(2017).
High-Fidelity Preparation, Gates, Memory, and Readout of a Trapped-Ion Quantum Bit
T. P. Harty, D. T. C. Allcock, C. J. Ballance, L. Guidoni, H. A. Janacek, N. M. Linke, D. N. Stacey, and D. M. Lucas Phys. Rev. Lett. 113, 220501 (2014).
Implementation of the semiclassical quantum Fourier transform in a scalable system
J. Chiaverini, J. Britton, D. Leibfried, E. Knill, M. D. Barrett, R. B. Blakestad, W. M. Itano, J. D. Jost, C. Langer, R. Ozeri, T. Schaetz, D. J. Wineland Science 308, 997 (2005).
A quantum information processor with trapped ions
P. Schindler, D. Nigg, T. Monz, J. T. Barreiro, E. Martinez, S. X. Wang, S. Quint, M. F. Brandl, V. Nebendahl, C. F. Roos, M. Chwalla, M. Hennrich and R. Blatt New Journal of Physics 15, 123012 (2013).
Realization of a scalable Shor algorithm
Thomas Monz, Daniel Nigg, Esteban A. Martinez, Matthias F. Brandl, Philipp Schindler, Richard Rines, Shannon X. Wang, Isaac L. Chuang, Rainer Blatt Science 351, 1068 (2016).
Realization of quantum error correction
J. Chiaverini, D. Leibfried, T. Schaetz, M. D. Barrett, R. B. Blakestad, J. Britton,W.M. Itano, J. D. Jost, E. Knill, C. Langer, R. Ozeri, D. J. Wineland Nature 432, 602 (2004).
Experimental repetitive quantum error correction
P. Schindler, J. T. Barreiro, T. Monz, V. Nebendahl, D. Nigg, M. Chwalla, M. Hennrich, and R. Blatt Science 332, 1059-1061 (2011).
Quantum computations on a topologically encoded qubit
D. Nigg, M. Müller, E. A. Martinez, P. Schindler, M. Hennrich, T. Monz, M. A. Martin-Delgado, R. Blatt Science 345, 302 (2014).
Sub-microsecond entangling gate between trapped ions via Rydberg interaction
Chi Zhang, Fabian Pokorny, Weibin Li, Gerard Higgins, Andreas Pöschl, Igor Lesanovsky, Markus Hennrich arXiv:1908.11284.
Our previous key results on quantum computation with trapped ions.
A completely list of publications from the Quantum Optics and Spectroscopy Group at University of Innsbruck can be found here.
A quantum information processor with trapped ions
P. Schindler, D. Nigg, T. Monz, J. T. Barreiro, E. Martinez, S. X. Wang, S. Quint, M. F. Brandl, V. Nebendahl, C. F. Roos, M. Chwalla, M. Hennrich and R. Blatt New Journal of Physics 15, 123012 (2013).
14-qubit entanglement: creation and coherence
T. Monz, P. Schindler, J.T. Barreiro, M. Chwalla, D. Nigg, W.A. Coish, M. Harlander, W. Hänsel, M. Hennrich, and R. Blatt Physical Review Letters 106, 130506 (2011).
An open-system quantum simulator with trapped ions
J. T. Barreiro, M. Müller, P. Schindler, D. Nigg, T. Monz, M. Chwalla, M. Hennrich, C. F. Roos, P. Zoller, and R. Blatt Nature 470, 486-491(2011).
Universal digital quantum simulation with trapped ions
B. P. Lanyon, C. Hempel, D. Nigg, M. Müller, R. Gerritsma, F. Zähringer, P. Schindler, J. T. Barreiro, M. Rambach, G. Kirchmair, M. Hennrich, P. Zoller, R. Blatt, C. F. Roos Science 334, 57-61 (2011).
Quantum simulation of dynamical maps with trapped ions
P. Schindler, M. Müller, D. Nigg, J. T. Barreiro, E. A. Martinez, M. Hennrich, T. Monz, S. Diehl, P. Zoller, R. Blatt, Nature Physics 9, 361–367 (2013).
Quantum computations on a topologically encoded qubit
D. Nigg, M. Müller, E. A. Martinez, P. Schindler, M. Hennrich, T. Monz, M. A. Martin-Delgado, R. Blatt Science 345, 302 (2014).
Experimental repetitive quantum error correction
P. Schindler, J. T. Barreiro, T. Monz, V. Nebendahl, D. Nigg, M. Chwalla, M. Hennrich, and R. Blatt Science 332, 1059-1061 (2011).
Demonstration of genuine multipartite entanglement with device-independent witnesses
J. T. Barreiro, J.-D. Bancal, P. Schindler, D. Nigg, M. Hennrich, T. Monz, N. Gisin, R. Blatt Nature Physics 9, 559–562 (2013).
Experimental multiparticle entanglement dynamics induced by decoherence
J.T. Barreiro, P. Schindler, O. Gühne, T. Monz, M. Chwalla, C.F. Roos, M. Hennrich, and R. Blatt Nature Physics 6, 943–946 (2010).