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Oscillator-to-oscillator codes do not have a threshold

Lisa Hanggli
Ludwig-Maximilians-Universitiät München (LMU)
June 16, 2021

PIRSA:21060003
Quantum Information
Quantum measurements of time

Lorenzo Maccone
University of Pavia
June 16, 2021

PIRSA:21060100
Quantum Foundations
(Quantum) frame covariance: from foundations via gauge theories to gravity

Philipp Hoehn
Okinawa Institute of Science and Technology Graduate University
June 16, 2021

PIRSA:21060099
Quantum Foundations
TBA

Mikhail Solon
University of California, Los Angeles
June 15, 2021

PIRSA:21060000
Particle Physics
Discussion Session 2
June 15, 2021

PIRSA:21060127
Quantum Foundations
The emergence of quantum mechanics and space, from a fundamental, active time

Lee Smolin
Perimeter Institute for Theoretical Physics
June 15, 2021

PIRSA:21060098
Quantum Foundations
"TIME IN QUANTUM GRAVITY - From the fundamental level to the classical limit"

Claus Kiefer
Universität zu Köln
June 15, 2021

PIRSA:21060109
Quantum Foundations
Space and Time in a Lorentzian path integral

Bianca Dittrich
Perimeter Institute for Theoretical Physics
June 15, 2021

PIRSA:21060095
Quantum Foundations
A New Perspective on Time Reversal Motivated by Quantum Gravity

Abhay Ashtekar
Pennsylvania State University
June 15, 2021

PIRSA:21060094
Quantum Foundations
Discussion Session 1
June 14, 2021

PIRSA:21060092
Quantum Foundations
Quantum reference frames for space and space-time

Časlav Brukner
Institute for Quantum Optics and Quantum Information (IQOQI) - Vienna
June 14, 2021

PIRSA:21060091
Quantum Foundations
Non-causal Page-Wootters circuits

Veronika Baumann
Institute for Quantum Optics and Quantum Information (IQOQI) - Vienna
June 14, 2021

PIRSA:21060090
Quantum Foundations

Oscillator-to-oscillator codes do not have a threshold

Lisa Hanggli
Ludwig-Maximilians-Universitiät München (LMU)
June 16, 2021

PIRSA:21060003
Quantum Information
It is known that continuous variable quantum information cannot be protected against naturally occurring noise using Gaussian states and operations only. Noh et al. (PRL 125:080503, 2020) proposed bosonic oscillator-to-oscillator codes relying on non-Gaussian resource states as an alternative, and showed that these encodings can lead to a reduction of the effective error strength at the logical level as measured by the variance of the classical displacement noise channel. An oscillator-to-oscillator code embeds K logical bosonic modes (in an arbitrary state) into N physical modes by means of a Gaussian N-mode unitary and N-K auxiliary one-mode Gottesman-Kitaev-Preskill-states.
Here we ask if - in analogy to qubit error-correcting codes - there are families of oscillator-to-oscillator codes with the following threshold property: They allow to convert physical displacement noise with variance below some threshold value to logical noise with variance upper bounded by any (arbitrary) constant. We find that this is not the case if encoding unitaries involving a constant amount of squeezing and maximum likelihood error decoding are used. We show a general lower bound on the logical error probability which is only a function of the amount of squeezing and independent of the number of modes. As a consequence, any physically implementable family of oscillator-to-oscillator codes combined with maximum likelihood error decoding does not admit a threshold.
Quantum measurements of time

Lorenzo Maccone
University of Pavia
June 16, 2021

PIRSA:21060100
Quantum Foundations
"We propose a time-of-arrival operator in quantum mechanics by conditioning on a quantum clock. This allows us to bypass some of the problems of previous proposals, and to obtain a Hermitian time of arrival operator whose probability distribution arises from the Born rule and which has a clear physical interpretation. The same procedure can be employed to measure the ""time at which some event happens"" for arbitrary events (and not just specifically for the arrival time of a particle). This talk is based on the paper: L. Maccone, K. Sacha, Quantum measurements of time, Phys. Rev. Lett. 124, 110402 (2020)."
(Quantum) frame covariance: from foundations via gauge theories to gravity

Philipp Hoehn
Okinawa Institute of Science and Technology Graduate University
June 16, 2021

PIRSA:21060099
Quantum Foundations
I will sketch how the perspective-neutral approach to (quantum) frame covariance brings together some recent developments on dynamical reference frames in quantum foundations, gauge theories and gravity. The survey will touch on spatial frames, quantum clocks and the problem of time, edge modes, and the relativity of subsystems.
TBA

Mikhail Solon
University of California, Los Angeles
June 15, 2021

PIRSA:21060000
Particle Physics
Abstract: TBD

Zoom Link: https://pitp.zoom.us/j/96516977019?pwd=WVlpZG5WTTUwbFJVZ2wvcXdNWUR5Zz09
Discussion Session 2
June 15, 2021

PIRSA:21060127
Quantum Foundations
The emergence of quantum mechanics and space, from a fundamental, active time

Lee Smolin
Perimeter Institute for Theoretical Physics
June 15, 2021

PIRSA:21060098
Quantum Foundations
"We propose a realist completion of quantum mechanics, in the sense of a complete description of individual events. The proposed fundamental theory assumes that time, events, causal structure, momentum and energy are fundamental. But space and the wave function are emergent. The beables of the theory are the views of the events, which are a subset of their causal pasts. Thus, this theory asserts that the universe is a causal network of events, which consists of partial views of itself as seen by looking backwards from each event. The theory is based on a simple action principle, which extremizes the variety of the universe, which is a measure of the diversity of its partial views. The Schroedinger equation is derived, while to higher order, there are computable corrections, non-linear in the wave function, from which new physical effects may be predicted. Finally, a relativistic version is sketched, in wqhich the views are built on the celestial sphere. "
"TIME IN QUANTUM GRAVITY - From the fundamental level to the classical limit"

Claus Kiefer
Universität zu Köln
June 15, 2021

PIRSA:21060109
Quantum Foundations
Time cannot be both absolute (as in quantum mechanics) and dynamical (as in general relativity). I present general arguments for the absence of time at the most fundamental level of quantum gravity. I discuss possible concepts that could replace it and present the recovery of standard time as an approximate concept. My discussion is restricted to quantum geometrodynamics, but I argue for the validity of my conclusions beyond that scheme.
Space and Time in a Lorentzian path integral

Bianca Dittrich
Perimeter Institute for Theoretical Physics
June 15, 2021

PIRSA:21060095
Quantum Foundations
I will present a quantum gravity approach based on a Lorentzian path integral for quantum geometries. The properties of quantum space time can be measured using geometric operators. This allows also to discuss fluctuations of causal structure as well as violations of (micro-) causality. I will explain how the Lorentzian path integral comes with various options regarding which quantum space times to sum over: e.g. whether to include causality violations or not, or whether to allow also for space times with Euclidean signatures in Lorentzian path integrals. I will sketch some consequences for the resulting theories.
A New Perspective on Time Reversal Motivated by Quantum Gravity

Abhay Ashtekar
Pennsylvania State University
June 15, 2021

PIRSA:21060094
Quantum Foundations
Time Reversal T is usually discussed in the traditional framework of quantum mechanics in which T is represented by an anti-unitary operator. But quantum gravity may well need generalization of standard quantum mechanics which may not preserve even its linear structure, let alone the unitarity of dynamics and anti-unitarity of T. Then the currently used arguments to conclude that T violation is a fundamental aspect of Nature will break down. Fortunately, it turns out that one can analyze the T-violation experiments in a much more general setting, of which classical and quantum mechanics are special cases. The setting does not require a Hilbert space, or linearity of either dynamics or symmetry operations such as T. Nonetheless, somewhat surprisingly, one would still be to use the current experiments to conclude that there is T violation at a fundamental level under rather minimal assumptions on the structure of the final quantum gravity theory.
Discussion Session 1
June 14, 2021

PIRSA:21060092
Quantum Foundations
Quantum reference frames for space and space-time

Časlav Brukner
Institute for Quantum Optics and Quantum Information (IQOQI) - Vienna
June 14, 2021

PIRSA:21060091
Quantum Foundations
In physics, a reference frame is an abstract coordinate system that specifies observations within that frame. While quantum states depend on the choice of reference frame, the form of physical laws is assumed to be covariant. Recently, it has been proposed to consider reference frames as physical systems and as such assume that they obey quantum mechanics. In my talk, I will present recent results in the field of "quantum reference frames" (QRF). In particular, I will formulate the covariance of dynamical physical laws with respect to non-relativistic QRF transformations and show how relativistic QRFs can be used to solve a long-standing problem in relativistic quantum information or to address typical quantum gravity scenarios.
Non-causal Page-Wootters circuits

Veronika Baumann
Institute for Quantum Optics and Quantum Information (IQOQI) - Vienna
June 14, 2021

PIRSA:21060090
Quantum Foundations
"The process matrix framework was invented to capture a phenomenon known as indefinite or quantum causal structure. Due to the generality of that framework, however, for many process matrices there is no clear physical interpretation. A popular approach towards a quantum theory of gravity is the Page-Wootters formalism, which associates to time a Hilbert space structure similar to spatial position. By explicitly introducing a quantum clock, it allows to describe time-evolution of systems via correlations between this clock and said systems encoded in history states. We combine the process matrix framework with a generalization of the Page-Wootters formalism in which one considers several observers, each with their own discrete quantum clock. This allows for implementing processes with indefinite casual order. The description via a history state with multiple clocks imposes constraints on the implementability of process matrices intros framework and on the perspectives of the observers. We describe how to to implement processes were the different definite causal orders are coherently controlled and explain why certain non-causal processes might not be implementable within this setting."

Title	Date	Collection	Type	Info
Oscillator-to-oscillator codes do not have a threshold	2021‑06‑16	Perimeter Institute Quantum Discussions	Scientific Series	View details
Quantum measurements of time	2021‑06‑16	Quantizing Time	Conference	View details
(Quantum) frame covariance: from foundations via gauge theories to gravity	2021‑06‑16	Quantizing Time	Conference	View details
TBA	2021‑06‑15	Particle Physics	Scientific Series	View details
Discussion Session 2	2021‑06‑15	Quantizing Time	Conference	View details
The emergence of quantum mechanics and space, from a fundamental, active time	2021‑06‑15	Quantizing Time	Conference	View details
"TIME IN QUANTUM GRAVITY - From the fundamental level to the classical limit"	2021‑06‑15	Quantizing Time	Conference	View details
Space and Time in a Lorentzian path integral	2021‑06‑15	Quantizing Time	Conference	View details
A New Perspective on Time Reversal Motivated by Quantum Gravity	2021‑06‑15	Quantizing Time	Conference	View details
Discussion Session 1	2021‑06‑14	Quantizing Time	Conference	View details
Quantum reference frames for space and space-time	2021‑06‑14	Quantizing Time	Conference	View details
Non-causal Page-Wootters circuits	2021‑06‑14	Quantizing Time	Conference	View details

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