Journal Article: Time dilation in quantum systems and decoherence
Pikovski, Igor, Zych, Magdalena, Costa, Fabio and Brukner, Časlav (2017) Time dilation in quantum systems and decoherence. New Journal of Physics, 19 2: . doi:10.1088/1367-2630/aa5d92
Journal Article: Multipartite causal correlations: polytopes and inequalities
Abbott, Alastair A., Giarmatzi, Christina, Costa, Fabio and Branciard, Cyril (2016) Multipartite causal correlations: polytopes and inequalities. Physical Review A, 94 3: 032131-1-032131-12. doi:10.1103/PhysRevA.94.032131
Journal Article: Experimental test of nonlocal causality
Ringbauer, Martin, Giarmatzi, Christina, Chaves, Rafael, Costa, Fabio, White, Andrew G. and Fedrizzi, Alessandro (2016) Experimental test of nonlocal causality. Science Advances, 2 8: . doi:10.1126/sciadv.1600162
Principles and applications of quantum causal discovery
(2017–2020) ARC Discovery Early Career Researcher Award
Quantum Causal Structures (Templeton Grant administered by Austrian Academy of Sciences)
(2016–2019) Austrian Academy of Sciences
All fundamental interactions known in nature are local: only close-by systems can interact. But where does the very notion of closeness come from? Ultimately, we only learn about spatial relations through physical systems, it should thus be possible to understand the locality of interactions without pre-assuming the existence of an absolute space.
The aim of the project is to derive the local structure of quantum systems from properties of dynamics alone, with no reference to any underlying geometry. Formally, the task is to derive a decomposition of Hilbert space in tensor factors, with each factor representing a local subsystem, from basis-independent properties of the Hamiltonian.
Available as Honours Project.
Quantum Information on indefinite causal structure
Quantum information has developed in the last decades into a broad field, offering several promising applications for future technology and deep insights into the foundations of physics. Very recently, first steps have been made in the direction of theoretically characterising and experimentally manipulating causal relations between quantum systems from an information-theoretical perspective. The motivations are two-fold: from a foundational perspective, it is expected that the notion of definite, classical causal structure would not survive in a theory where gravity, and thus space-time, are subject to quantum effects. More practically, it has been proposed that quantum causal relations can also be realised in laboratory experiments and that they can provide advantage for several tasks, such as computation and communication complexity.
As this is a very new field, it still needs development of basic tools and exemplary protocols. To name but a few possibilities:
· Communication: how does indefinite causal structure affect the possibility of communicating classical or quantum information?
· Discrimination of causal structure: Given a set of events and some prior information about their causal relations, what are the optimal protocols for inferring the causal structure?
· Teleportation of causal structure: is it possible to exploit “entangled causal relations” to effectively teleport an unknown causal structure from a set of events to another?
· Information measures on indefinite causal structure: what are meaningful ways to quantify information encoded in systems with indefinite causal structure? Is it possible to quantify information about the causal structure itself?
The aim of the project is to develop some of these tools, having in mind potential applications to information-theoretical tasks, quantum technologies, or foundational questions.
Available both as Honours or PhD Project.
Classical indeterminism near closed time-like curves
General relativity predicts the possibility of space-time geometries that contain closed time-like curves (CTCs), along which a particle could travel back in time and interact with its past self. Studies of simple bouncing billiard balls along CTCs have revealed a surprising feature: Given the initial position and velocity of the ball, there are typically multiple solutions of the equations of motion, namely many different trajectories compatible with the initial conditions [1]. This result is in striking contrast with the determinism traditionally associated with classical physics and opens the question of what type of predictions are possible in the presence of CTCs.
The aim of this project is to develop a method to make probabilistic predictions for classical systems near CTCs, both considering specific examples—such as the billiard ball problem [1]—and developing a general formalism. The results will be compared with those derived from a quantum-mechanical modelling of the problem [2].
The project requires a basic knowledge of the formalism of General Relativity and possibly of the path-integral formulation of quantum mechanics.
[1] F. Echeverria, G. Klinkhammer, and K. S. Thorne, Phys. Rev. D 44, 1077 (1991).
[2] H. D. Politzer, Phys. Rev. D 49, 3981 (1994).
Time dilation in quantum systems and decoherence
Pikovski, Igor, Zych, Magdalena, Costa, Fabio and Brukner, Časlav (2017) Time dilation in quantum systems and decoherence. New Journal of Physics, 19 2: . doi:10.1088/1367-2630/aa5d92
Multipartite causal correlations: polytopes and inequalities
Abbott, Alastair A., Giarmatzi, Christina, Costa, Fabio and Branciard, Cyril (2016) Multipartite causal correlations: polytopes and inequalities. Physical Review A, 94 3: 032131-1-032131-12. doi:10.1103/PhysRevA.94.032131
Experimental test of nonlocal causality
Ringbauer, Martin, Giarmatzi, Christina, Chaves, Rafael, Costa, Fabio, White, Andrew G. and Fedrizzi, Alessandro (2016) Experimental test of nonlocal causality. Science Advances, 2 8: . doi:10.1126/sciadv.1600162
Costa, Fabio and Shrapnel, Sally (2016) Quantum causal modelling. New Journal of Physics, 18 6: . doi:10.1088/1367-2630/18/6/063032
The simplest causal inequalities and their violation
Branciard, Cyril Branciard, Araujo, Mateus, Feix, Adrien, Costa, Fabio and Brukner, Caslav (2015) The simplest causal inequalities and their violation. New Journal of Physics, 18 1: . doi:10.1088/1367-2630/18/1/013008
Witnessing causal nonseparability
Araujo, Mateus, Branciard, Cyril, Costa, Fabio, Feix, Adrien, Giarmatzi, Christina and Brukner, Caslav (2015) Witnessing causal nonseparability. New Journal of Physics, 17 10: . doi:10.1088/1367-2630/17/10/102001
Experimental superposition of orders of quantum gates
Procopio, Lorenzo M., Moqanaki, Amir, Araujo, Mateus, Costa, Fabio, Calafell, Irati A., Dowd, Emma G., Hamel, Dendy R., Rozema, Lee A., Brukner, Caslav and Walther, Philip (2015) Experimental superposition of orders of quantum gates. Nature Communications, 6 7913: 1-6. doi:10.1038/ncomms8913
Universal decoherence due to gravitational time dilation
Pikovski, Igor, Zych, Magdalena, Costa, Fabio and Brukner, Caslav (2015) Universal decoherence due to gravitational time dilation. Nature Physics, 11 8: 668-672. doi:10.1038/nphys3366
Computational advantage from quantum-controlled ordering of gates
Araujo, Mateus, Costa, Fabio and Brukner, Caslav (2014) Computational advantage from quantum-controlled ordering of gates. Physical Review Letters, 113 25: 250402-1-250402-5. doi:10.1103/PhysRevLett.113.250402
Renormalized entropy of entanglement in relativistic field theory
Ibnouhsein, Issam, Costa, Fabio and Grinbaum, Alexei (2014) Renormalized entropy of entanglement in relativistic field theory. Physical Review D, 90 . doi:10.1103/PhysRevD.90.065032
Quantum circuits cannot control unknown operations
Araujo, Mateus, Feix, Adrien, Costa, Fabio and Brukner, Caslav (2014) Quantum circuits cannot control unknown operations. New Journal of Physics, 16 . doi:10.1088/1367-2630/16/9/093026
General relativistic effects in quantum interference of photons
Zych, Magdalena, Costa, Fabio, Pikovski, Igor, Ralph, Timothy C. and Brukner, Caslav (2012) General relativistic effects in quantum interference of photons. Classical and Quantum Gravity, 29 22: 224010-1-224010-18. doi:10.1088/0264-9381/29/22/224010
Quantum correlations with no causal order
Oreshkov, Ognyan, Costa, Fabio and Brukner, Caslav (2012) Quantum correlations with no causal order. Nature Communications, 3 . doi:10.1038/ncomms2076
Quantum interferometric visibility as a witness of general relativistic proper time
Zych, Magdalena, Costa, Fabio, Pikovski, Igor and Brukner, Caslav (2011) Quantum interferometric visibility as a witness of general relativistic proper time. Nature Communications, 2 1: . doi:10.1038/ncomms1498
Entanglement between smeared field operators in the Klein-Gordon vacuum
Zych, Magdalena, Costa, Fabio, Kofler, Johannes and Brukner, Caslav (2010) Entanglement between smeared field operators in the Klein-Gordon vacuum. Physical Review D: covering particles, fields, gravitation, and cosmology, 81 12: . doi:10.1103/PhysRevD.81.125019
Entanglement detection with bounded reference frames
Costa, Fabio, Harrigan, Nicholas, Rudolph, Terry and Brukner, Caslav (2009) Entanglement detection with bounded reference frames. New Journal of Physics, 11 . doi:10.1088/1367-2630/11/12/123007
Modeling a particle detector in field theory
Costa, Fabio and Piazza, Federico (2009) Modeling a particle detector in field theory. New Journal of Physics, 11 . doi:10.1088/1367-2630/11/11/113006
Renormalized thermal entropy in field theory
Cacciatori, Sergio L., Costa, Fabio and Piazza, Federico (2009) Renormalized thermal entropy in field theory. Physical Review D, 79 2: . doi:10.1103/PhysRevD.79.025006
General relativistic effects in quantum interference of "clocks"
Zych, M., Pikovski, I., Costa, F. and Brukner, C. (2016). General relativistic effects in quantum interference of "clocks". In: 8th Symposium on Frequency Standards and Metrology 2015. 8th Symposium on Frequency Standards and Metrology 2015, Potsdam, Germany, (). 12 - 16 October 2015. doi:10.1088/1742-6596/723/1/012044
Principles and applications of quantum causal discovery
(2017–2020) ARC Discovery Early Career Researcher Award
Quantum Causal Structures (Templeton Grant administered by Austrian Academy of Sciences)
(2016–2019) Austrian Academy of Sciences
Note for students: The possible research projects listed on this page may not be comprehensive or up to date. Always feel free to contact the staff for more information, and also with your own research ideas.
All fundamental interactions known in nature are local: only close-by systems can interact. But where does the very notion of closeness come from? Ultimately, we only learn about spatial relations through physical systems, it should thus be possible to understand the locality of interactions without pre-assuming the existence of an absolute space.
The aim of the project is to derive the local structure of quantum systems from properties of dynamics alone, with no reference to any underlying geometry. Formally, the task is to derive a decomposition of Hilbert space in tensor factors, with each factor representing a local subsystem, from basis-independent properties of the Hamiltonian.
Available as Honours Project.
Quantum Information on indefinite causal structure
Quantum information has developed in the last decades into a broad field, offering several promising applications for future technology and deep insights into the foundations of physics. Very recently, first steps have been made in the direction of theoretically characterising and experimentally manipulating causal relations between quantum systems from an information-theoretical perspective. The motivations are two-fold: from a foundational perspective, it is expected that the notion of definite, classical causal structure would not survive in a theory where gravity, and thus space-time, are subject to quantum effects. More practically, it has been proposed that quantum causal relations can also be realised in laboratory experiments and that they can provide advantage for several tasks, such as computation and communication complexity.
As this is a very new field, it still needs development of basic tools and exemplary protocols. To name but a few possibilities:
· Communication: how does indefinite causal structure affect the possibility of communicating classical or quantum information?
· Discrimination of causal structure: Given a set of events and some prior information about their causal relations, what are the optimal protocols for inferring the causal structure?
· Teleportation of causal structure: is it possible to exploit “entangled causal relations” to effectively teleport an unknown causal structure from a set of events to another?
· Information measures on indefinite causal structure: what are meaningful ways to quantify information encoded in systems with indefinite causal structure? Is it possible to quantify information about the causal structure itself?
The aim of the project is to develop some of these tools, having in mind potential applications to information-theoretical tasks, quantum technologies, or foundational questions.
Available both as Honours or PhD Project.
Classical indeterminism near closed time-like curves
General relativity predicts the possibility of space-time geometries that contain closed time-like curves (CTCs), along which a particle could travel back in time and interact with its past self. Studies of simple bouncing billiard balls along CTCs have revealed a surprising feature: Given the initial position and velocity of the ball, there are typically multiple solutions of the equations of motion, namely many different trajectories compatible with the initial conditions [1]. This result is in striking contrast with the determinism traditionally associated with classical physics and opens the question of what type of predictions are possible in the presence of CTCs.
The aim of this project is to develop a method to make probabilistic predictions for classical systems near CTCs, both considering specific examples—such as the billiard ball problem [1]—and developing a general formalism. The results will be compared with those derived from a quantum-mechanical modelling of the problem [2].
The project requires a basic knowledge of the formalism of General Relativity and possibly of the path-integral formulation of quantum mechanics.
[1] F. Echeverria, G. Klinkhammer, and K. S. Thorne, Phys. Rev. D 44, 1077 (1991).
[2] H. D. Politzer, Phys. Rev. D 49, 3981 (1994).