Distributed Quantum Systems
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Our Team
PhD defense of Dr. Meraner, in direct sunlight. From left to right: Ben Lanyon, Josef Schupp, Zhe Koong, Armin Winkler, Marco Canteri, Viktor Krutianskii, Martin Meraner, James Bate, Vojtech Krcmarksy, Tabea Stroinski, Johannes Helgert
Tabea Stroinski (master)
Johannes Helgert (master)
Armin Winkler (master)
Pascal Wintermeyer (master)
James Bate (PhD)
Marco Canteri (Master student)
Vojtech Krcmarsky (PhD)
Zhe Koong (Postdoc)
Viktor Krutianskii (Postdoc)
Ben Lanyon (Project Leader)
Former project members
Dr. Martin Meraner (PhD)
Dr. Josef Schupp (PhD)
Helene Hainzer (Master Student), now in group of Ch. Roos, working on quantum simulations with 2D ion crystals
Dr. Muir Kumph (Postdoc), now IBM Watson Research Centre
Publications
 A telecomwavelength quantum repeater node based on a trappedion processor
Victor Krutyanskiy, Marco Canteri, Martin Meraner, James Bate, Vojtech Krcmarsky, Josef Schupp, Nicolas Sangouard, Ben P. Lanyon
arXiv:2210.05418  Entanglement of trappedion qubits separated by 230 meters
V. Krutyanskiy, M. Galli, V. Krcmarsky, S. Baier, D. A. Fioretto, Y. Pu, A. Mazloom, P. Sekatski, M. Canteri, M. Teller, J. Schupp, J. Bate, M. Meraner, N. Sangouard, B. P. Lanyon, T. E. Northup
arXiv:2208.14907  Interface between TrappedIon Qubits and Traveling Photons with ClosetoOptimal Efficiency
J. Schupp, V. Krcmarsky, V. Krutyanskiy, M. Meraner, T.E. Northup, and B.P. Lanyon
PRX Quantum 2, 020331 (2021)  Indistinguishable photons from a trappedion quantum network node
M. Meraner, A. Mazloom, V. Krutyanskiy, V. Krcmarsky, J. Schupp, D. A. Fioretto, P. Sekatski, T. E. Northup, N. Sangouard, and B. P. Lanyon
Phys. Rev. A 102, 052614 (2020)  Lightmatter entanglement over 50 km of optical fibre
V. Krutyanskiy, M. Meraner, J. Schupp, V. Krcmarsky, H. Hainzer & B. P. Lanyon
npj Quantum Information, volume 5, Article number: 72 (2019)  Deterministic quantum state transfer between remote qubits in cavities
B. Vogell, B. Vermersch, T. E. Northup, B. P. Lanyon, C. A. Muschik
Quantum Sci. Technol. 2 045003, arXiv:1704.06233
 "Polarisationpreserving photon frequency conversion from a trappedioncompatible wavelength to the telecom Cband"
V. Krutyanskiy, M. Meraner, J. Schupp and B. P. Lanyon
Appl. Phys. B 123, 228 (2017) (Open access)  "Quantum repeaters based on trapped ions with decoherencefree subspace encoding"
M. Zwerger, B. P. Lanyon, T. E. Northup, C. A. Muschik, W. Dür and N. Sangouard
Quantum Sci. Technol.2 (2017),arXiv:1611.07779
FWF START project
Our group was founded following the award of an FWF START project entitled 'Quantum Frequency Conversion for Trapped ion Quantum Networks' in 2015. In this project, we investigate a way to interface light with the quantum states of trapped atomic ions. Our approach is to exploit a nonlinear optical process to change the frequency of single photons emitted and absorbed by trapped ions, from their natural values to those that are optimal for quantum networking. This frequencyshifter could act as a universal adapter for accessing and distributing the quantum states of trapped ions: between different traps and other quantum systems. Our experiments combine single photon nonlinear optics, atomic physics, cavity quantum electrodynamics (cavity QED), and quantum information science.
Why change the photons emitted by trapped ions?
Trapped atomic ions provide an excellent system with which to investigate and engineer quantum phenomena [1]. Photons, which are emitted and absorbed by trapped ions, can be used to interface with and distribute the quantum states of the ions. Photons could thus be used to establish quantum links between remote networks of trapped ions, or between ions and other examples of quantum matter [2]. Developing such quantum networks further would open up new directions in fields of quantum metrology, communication and computation: for new scientific tools, technology and for fundamental science [3]. Indeed, ions in traps a few meters apart have been quantum linked (entangled) via the exchange of single photons at their natural frequency [4], and recently the first coupling between an ion and a quantum dot has been observed [5]. Extending these ideas further opens up many new research challenges, two of which we aim to tackle in our work:
The photon absorption problem: The photons readily emitted by trapped ions are typically at frequencies that are strongly absorbed in optical fiber and the atmosphere. This limits the distance that such photons can distribute quantum correlations and information.
The photon mismatch problem: Different examples of quantum matter (such as ion, atoms or quantum dots) typically emit and absorb photons at specific and incompatible frequencies. This represents an obstacle to interfacing different kinds of systems at a quantum level.
A possible solution to these problems is to develop a tool that allows the frequency of photons emitted by ions to be changed, whilst preserving their quantum properties. Such a tool would allow the photons emitted by trapped ions to be shifted to the points of minimal absorption in optical waveguides and to values directly compatible with other quantum systems.
A photonic quantum adapter for trapped ions. A nonlinear process allows the frequency of single photons to be tuned over a broad range of values: from those with minimal transmission loss, to those compatible with other kinds of quantum matter.
How can the frequency of a single photon be changed?
Our approach is to exploit the process of difference frequency generation (DFG) mediated by a crystal with a nonlinear response to light.
The process of difference frequency generation mediated by a material with a nonlinear response to light. Coupling the photon and pump laser field into waveguides integrated into the nonlinear material, could enable near unit conversion efficiency. In our lab we explore both ridge & buried waveguide approaches.
A single photon (frequency f_{1}) enters the crystal, overlapped with a strong classical ‘pump’ laser field (frequency f_{pump}). Ideally, the single photon emerges from the crystal with a new frequency f_{2}, that is reduced by that of the pump (f_{2 }= f_{1 } f_{pump}). Overall, this process could be used to convert high energy (frequency) photons emitted by trapped ions, to lower energies that are more useful sending over long distance and talking to other quantum systems. The process should be fully reversible, allowing photon energies to be increased again then for reabsorbtion by quantum matter.
There has already been a lot of theoretical and experiment work on single photon frequency conversion in other contexts (see below). The new challenges for us are to apply this technique to the kinds of photons emitted by ions and to do so with high efficiency and low noise. Furthermore, all the spectral, temporal and quantum properties of the photons (other than the central frequency) should be preserved through the conversion process. This will require new levels of control over both the trappedion and the conversion process.
We will exploit the emerging technology of waveguideintegrated nonlinear crystals. Here, micron scale waveguides are integrated into the crystal, defined by either a localised dopant, or geometrically by milling out ridges.
Our main experimental goals
We aim to learn as much as possible about the photon conversion technique and its potential to open up new ways to interface with trapped ions. We have two main experimental goals over the next five years. First, we aim to observe entanglement between an ion and a frequencyconverted 1550 nm photon. 1550 nm is the wavelength with minimal loss in optic fiber, used by the global telecommunications industry. As such, 1550 nm (or other such ‘telecom bands’) would make an ideal frequency standard for interfacing quantum systems and building quantum networks. <spanSecond, we aim to observe entanglement between an ion and a photon that has been distributed over tens of kilometers of optical fiber. Distributed entanglement represents a fundamental resource for new science and technology.
Our experimental systems
There are two parts to the experimental systems in our lab, which are currently being set up. The first part is the nonlinear conversion system in which waveguide chips are combined with precision optics for in and outcoupling, highpower mid infrared pump lasers, narrowband optical filtering stages and single photon detectors.
Our second experimental system is a trappedion single photon source. Our source will combine an ion trap with an integrated optical cavity to achieve a neardeterministic and ondemand source of 854 nm photons that entangled with the electronic state of a calcium ion. Such a system exploits cavity quantum electrodynamic effects to stimulate photon emission into the cavity mode with high probability [6]. This system will generate photons for the frequency conversion project and will be one of three CQEDenhanced ion traps in Innsbruck that form a three node lightmatter quantum network (project 'SciNet'). In such a network the trapped calcium ions offer longlived quantum memories and deterministic quantum logic.
The trappedion single photon source that we have developed: a linearPaul ion trap (gold electrodes) with an integrated optical cavity (blue mirrors). The ion, or string of ions, is at the centre of the cavity mode (red). An ultraviolet laser pulse (not shown) triggers the emission of a single photon from an ion into the cavity mode, which then exits through a predetermined cavity mirror with high probability. Our system design is based on an established Innsbruck design [6] and optimised for highlyefficienct photon extraction.
The realization of our experimental setup.
References
Funding
This project is funded by the START programme of the Austrian Science Fund (Fonds zur Förderung der wissenschaftlichen Forschung, FWF)

Our team also receives support and funding from:
The Institute for Quantum Optics and Quantum Information (IQOQI) 
The Army Research Laboratory, of the USA 


Old team photos
Team in 2019. (from left to right: BL, HH, MM, MC, ViK, VoK, JS)