Chiara Greganti

University of Vienna | UniWien · Quantum Optics, Quantum Nanophysics and Quantum Information Group

Quantum computers are on the brink of surpassing the capabilities of even the most powerful classical computers, which naturally raises the question of how one can trust the results of a quantum computer when they cannot be compared to classical simulation Here, we present a cross-verification technique that exploits the principles of measurement-b...

A new entanglement-verification method is introduced and experimentally verified with a six-photon cluster state. We demonstrate that it is possible to efficiently detect multipartite entanglement with only a few copies of the state.

Many future quantum technologies rely on the generation of entangled states. Quantum devices will require verification of their operation below some error threshold, but the reliable detection of quantum entanglement remains a considerable challenge for large-scale quantum systems. Well-established techniques for this task rely on the measurement o...

In standard communication information is carried by particles or waves. Counterintuitively, in counterfactual communication particles and information can travel in opposite directions. The quantum Zeno effect allows Bob to transmit a message to Alice by encoding information in particles he never interacts with. A first remarkable protocol for count...

Quantum computers are on the brink of surpassing the capabilities of even the most powerful classical computers. This naturally raises the question of how one can trust the results of a quantum computer when they cannot be compared to classical simulation. Here we present a scalable verification technique that exploits the principles of measurement...

Entanglement verification becomes hard when dealing with large quantum systems. By treating this task probabilistically, we certify entanglement with high confidence in an experimental photonic six-qubit cluster state by using only a few detection events.

Accidental photon noise and imperfect single-photon purity in spontaneous parametric down-conversion (SPDC) at telecom wavelengths are overcome by exploiting a passive temporal multiplexing scheme and optimizing the spectral properties of the down- converted photons.

We introduce a new entanglement-verification method and use it to experimentally verify the entanglement in a photonic six-qubit cluster state, created at telecommunication wavelengths, by detecting only 20 copies of the quantum state.

Quantum technologies lead to a variety of applications that outperform their classical counterparts. In order to build a quantum device it must be verified that it operates below some error threshold. Recently, because of technological developments which allow for the experimental realization of quantum states with increasing complexity, these task...

In standard communication information is carried by particles or waves. Counterintuitively, in counterfactual communication particles and information can travel in opposite directions. The quantum Zeno effect allows Bob to transmit a message to Alice by encoding information in particles he never interacts with. The first suggested protocol not only...

Multi-photon state generation is of great interest for near-future quantum simulation and quantum computation experiments. To-date spontaneous parametric down-conversion is still the most promising process, even though two major impediments still exist: accidental photon noise (caused by the probabilistic non-linear process) and imperfect single-ph...

The vast development of integrated quantum photonic technology enables the implementation of compact and stable interferometric networks. In particular, laser-written waveguide structures allow for complex 3D circuits and polarization-encoded qubit manipulation. However, the main limitation in the scaling up of integrated quantum devices is the sin...

The vast development of integrated quantum photonic technology enables the implementation of compact and stable interferometric networks. In particular laser-written waveguide structures allow for complex 3D-circuits and polarization-encoded qubit manipulation. However, the main limitation for the scale-up of integrated quantum devices is the singl...

We present a detailed numerical investigation of five nonlinear materials and their properties regarding photon-pair creation using parametric down-conversion. Periodic poling of ferroelectric nonlinear materials is a convenient way to generate collinearly propagating photon pairs. Most applications and experiments use the well-known potassium tita...

Blind quantum computing allows for secure cloud networks of quasi-classical clients and a fully fledged quantum server. Recently, a new protocol has been proposed, which requires a client to perform only measurements. We demonstrate a proof-of-principle implementation of this measurement-only blind quantum computing, exploiting a photonic setup to...

Vast developments in quantum technology have enabled the preparation of quantum states with more than a dozen entangled qubits. The full characterization of such systems demands distinct constructions depending on their specific type and the purpose of their use. Here we present a method that scales linearly with the number of qubits for characteri...

In measurement-based quantum computing an algorithm is performed by measurements on highly-entangled resource states. To date, several implementations were demonstrated, all of them assuming perfect noise-free environments. Here we consider measurement-based information processing in the presence of noise and demonstrate all elements of quantum err...

The simulation of open quantum dynamics has recently allowed the direct investigation of the features of system-environment interaction and of their consequences on the evolution of a quantum system. Such interaction threatens the quantum properties of the system, spoiling them and causing the phenomenon of decoherence. Sometimes however a coherent...

Supplementary Information

We report the experimental demonstration of two quantum networking protocols, namely quantum 1->3 telecloning and open-destination teleportation, implemented using a four-qubit register whose state is encoded in a high-quality two-photon hyperentangled Dicke state. The state resource is characterized using criteria based on multipartite entanglemen...

A two qubit quantum gate, namely the C-Phase, has been realized by exploiting the longitudinal momentum (i.e. the optical path) degree of freedom of a single photon. The experimental setup used to engineer this quantum gate represents an advanced version of the high stability closed-loop interferometric setup adopted to generate and characterize 2-...