We are the proud users of a small-scale ion-trap quantum computer. We use it to investigate new properties of quantum information processing and, more generally, fundamental properties of quantum physics. Our main research interests lie in identifying and implementing interesting problems, as well as developing scalable hardware, firmware, and software for a future quantum computer.
Linear ion trap: By applying voltages to the trap electrodes, a string of ions
can be held in the trap for several days. The lower picture shows a string
of 6 Calcium 40 ions taken with a ordinary CCD camera.
An ion-trap based quantum computer
In our experiment, we use single ions lined up in a chain as a quantum register to perform quantum information processing. The ions are trapped in a linear Paul trap as can be seen in the picture below. Each ion holds a quantum version of the smallest unit of information, a quantum bit (qubit). Unlike a classical computer bit, the qubit can be in a superposition state, which can be loosely described as being in two states at the same time. Such a superposition is not possible in a classical system and is the foundation of the computational power of a quantum computer. The generation of these superposition states onto a register with multiple qubits is "quantum entanglement", which is so counter intuitive that it was described by Einstein as a "spooky action". In our experiment we have demonstrated an entangled quantum register consisting of 14 qubits. (T. Monz et al)
Quantum algorithms
We have contributed in developing a set of operations that allows us to run any possible algorithm on a small-scale quantum register. These operations are similar to elementary logic gates in classical computers, but are inherently different as they allow us to generate highly entangled states of the quantum register. In order to facilitate the implementation of high-level quantum algorithms, we also work on a compiler for a quantum computer, that translates a given algorithm into a set of elementary quantum operations (Martinez et al.). Our research is driven by developing and optimizing these operations to run a quantum algorithm faithfully on a larger quantum register.
Quantum error correction
Theoretical research has shown that a large-scale quantum computer will need to be self-correcting. That means that small errors that are introduced during the algorithm are corrected immediately. Unlike classical computers, one cannot simply read out a qubit to check and correct for errors. Instead, more delicate procedures are required. We have demonstrated proof-of-concept experiments for such error correction procedures (P. Schindler et al, D. Nigg et al). However, an error correction scheme that will enable arbitrarily long quantum algorithms is still in the future. We are part of an international collaboration with the aim to demonstrate a useful quantum error correction procedure.
Motional Control
We are investigating shuttling, splitting and swapping the position of our ions. This motional control can be achieved by individually controlling the voltages applied to the segments of the trap to reshape the trapping potential. Rearranging the ion string enables selctively coupling and decoupling of qubits from entangling gates. This is a promising approach for building larger ion trap quantum computers, as the number of ions that can be stored in string configuration in a single potential well is limited.
The experiment table of the cryogenic setup.
Our experimental Platforms
We have two quantum processors available for our experiments. The linear trap is a macroscopic linear blade trap loaded with Calcium 40 ions. The setup is capable of producing high fidelity operations for both single and mult-quibt gates.
The second setup uses a microfabricated segmented trap inside a cryogenic environment (Brandl et al.). This trap can be loaded with both Calcium 40 and Strontium 88, with Strontium intended to serve as ancilla for sympathetic cooling and in-sequence readout. We are currently adapting the setup to accomodate a High Optical Access Trap from Sandia (P. Maunz).
View into the vacuum chamber with the linear ion trap inside. |
View of the segmented trap inside the cryostat through the addressing viewport. |
Research Highlights
- Lattice gauge theories
- Shor's algorithm
- Color Code
- Open system simulation
- 14 qubit entanglement
Project Members
- Julian Rickert (Master Student)
- Alexander Erhard (PhD student)
- Lukas Gerster (PhD student)
- Michael Meth (PhD student)
- Martin Van Mourik (PhD student)
- Lukas Postler (PhD student)
- Roman Stricker (PhD student)
- Tetsu Takekoshi (Postdoc)
- Thomas Monz (senior scientist)
- Philipp Schindler (senior scientist)
- Rainer Blatt (group leader)
Former members: Julio Barreiro, Michael Chwalla, Stefan Quint, Rafael Rothganger de Paiva, Virgile Andreani, Anton Nolf, Daniel Nigg, Matthias Brandl, Esteban Martinez