Seminar by Abolfazl Bayat


We are happy to announce our next seminar.

Speaker: Abolfazl Bayat (University of Electronic Science and Technology of China, CHN)
When: Thursday, 14th January 2020, 3PM (CET time)
Where: online (Zoom) zoom.us/my/aula.x


Title: Driving enhanced quantum sensing in partially accessible many-body systems

Abstract:
Ground state criticality of many-body systems is a resource for quantum enhanced sensing, namely Heisenberg precision limit, provided that one has access to the whole system. We show that for partial accessibility the sensing capacity of a block in the ground state reduces to sub-Heisenberg limit. To compensate for this, we drive the system periodically and use the local steady state for quantum sensing. Remarkably, the steady state sensing shows a significant enhancement in its precision in comparison with the ground state and even shows super-Heisenberg scaling for a certain range of frequencies. The origin of this precision enhancement is found to be the closing of the Floquet gap. This is in close correspondence with the role of the vanishing energy gap
at criticality for quantum enhanced ground state sensing with global accessibility.

SEMINAR BY Jan Chwedenczuk

We are happy to announce our next seminar.

Speaker: Jan Chwedenczuk (Warsaw University, POL)
When: Thursday, 7th January 2020, 3PM (CET time)
Where: online (Zoom) zoom.us/my/aula.x


Title: Many-body nonlocality as a resource for quantum-enhanced
metrology


Abstract:
In this talk I will argue that the strongest quantum correlation, manifested by a many-body nonlocality, is a resource for ultra-precise metrology. I will show that the sensitivity of a quantum sensor can be expressed in terms of many-body correlation functions (such that witness the nonlocality) of all orders. I will illustrate this general result with some prominent examples, such as a collection of spins forming an Ising chain or a gas of ultra-cold bosons in any two-mode configuration.


We are also glad to announce one more seminar
[ more details in the next weeks — SAVE THE DATE(S) ]

Speaker: Abolfazl Bayat (University of Electronic Science and Technology of China Chengdu, CHN)
When: Thursday, 14th January 2020, 3PM (CET time)
Where: online (Zoom) zoom.us/my/aula.x
Title: TBA

Seminar by Luca Razzoli

We are happy to announce our next seminar.

Speaker: Luca Razzoli (University of Modena & Reggio Emilia, ITA)
When: Thursday, 17th December 2020, 3PM (CET time)
Where: online (Zoom) zoom.us/my/aula.x


Title: Transport efficiency of continuous-time quantum walks on graphs

Abstract:
Continuous-time quantum walk describes the propagation of a quantum particle (or an excitation) evolving continuously in time on a graph. As such, it provides a natural framework for modeling transport processes, e.g., in light-harvesting systems. In particular, the transport properties strongly depend on the initial state and on the specific features of the graph under investigation. In this talk, we are going to address the role of graph topology, and investigate the transport properties of graphs with different regularity, symmetry, and connectivity. We neglect disorder and decoherence, and assume a single trap vertex accountable for the loss processes. In particular, for each graph, we analytically determine the subspace of states having maximum transport efficiency. Our results provide a set of
benchmarks for environment-assisted quantum transport, and suggest that connectivity is a poor indicator for transport efficiency. Indeed, we observe some specific correlations between transport efficiency and connectivity for certain graphs, but in general they are uncorrelated.


We are also glad to announce two more seminars
[ more details in the next weeks — SAVE THE DATE(S) ]

Speaker: Jan Chwedenczuk (Warsaw University, POL)
When: Thursday, 7th January 2020, 3PM (CET time)
Where: online (Zoom) zoom.us/my/aula.x
Title: Many-body nonlocality as a resource for quantum-enhanced
metrology

Speaker: Abolfazl Bayat (University of Electronic Science and Technology of China Chengdu, CHN)
When: Thursday, 14th January 2020, 3PM (CET time)
Where: online (Zoom) zoom.us/my/aula.x
Title: TBA

Seminar by Patrick Potts

We are happy to announce our next seminar.

Speaker: Patrick Potts (Lund University, SWE)
When: Thursday, 10th December 2020, 3PM (CET time)
Where: online (Zoom) zoom.us/my/aula.x

Title: Certifying nonclassical behavior for negative Keldysh
 quasiprobabilities


Abstract:
Quantum fluctuations behave fundamentally different from their classical counterparts. Due to the unavoidable measurement backaction in quantum mechanics, a measurement of multiple observables can in general not be described by a (positive) probability distribution that does not include the measurement apparatus explicitly. To describe fluctuations in the quantum regime without resorting to an explicit measurement apparatus, quasi-probability distributions which may become negative may be used. An example is provided by the Wigner function which generalizes the concept of phase space to quantum mechanics. Despite this difference between classical and quantum descriptions, it is a non-trivial task to decide if the fluctuations observed in an experiment arise from a classical or a quantum process. One reason for this is that measurement backaction, while avoidable in classical scenarios, may nevertheless be present. In this talk, I will show how one can rule out a classical description using an experimentally accessible inequality which is based on a few natural assumptions on the measurement apparatus. In quantum theory, this inequality can be violated if and only if a corresponding quasi-probabiliy distribution (called Keldysh quasi-probability distribution) becomes negative. Importantly, all assumptions on the detectors can be fulfilled in quantum theory, allowing for the conclusion that the measured data cannot be obtained from any classical process.


We are also glad to announce three more seminars
more details in the next weeks — SAVE THE DATE(S)

Speaker: Luca Razzoli (University of Modena & Reggio Emilia, ITA)
When: Thursday, 17th December 2020, 3PM (CET time)
Where: online (Zoom) zoom.us/my/aula.x
Title: Transport efficiency of continuous-time quantum walks on graphs

Speaker: Jan Chwedenczuk (Warsaw University, POL)
When: Thursday, 7th January 2020, 3PM (CET time)
Where: online (Zoom) zoom.us/my/aula.x
Title: Many-body nonlocality as a resource for quantum-enhanced
metrology

Speaker: Abolfazl Bayat (University of Electronic Science and Technology of China Chengdu, CHN)
When: Thursday, 14th January 2020, 3PM (CET time)
Where: online (Zoom) zoom.us/my/aula.x
Title: TBA

Seminar by Nathan Shammah

We are happy to announce our next seminars.

Speaker: Nathan Shammah (Unitary Fund)
When: Thursday, 26th November 2020, 3pm (CET)
Where: online (Zoom)  zoom.us/my/aula.x 

Title: Quantum error mitigation on noisy quantum computers
Abstract:
Error-mitigation techniques improve computational performance (with respect to noise) using minimal overhead in quantum resources by relying on a mixture of quantum sampling and classical post-processing techniques. In this talk I will provide a brief overview of error mitigation techniques and a hands-on introduction to an open-source package for error-mitigation in quantum computation, Mitiq [1,2], which implements zero-noise extrapolation and soon probabilistic error cancellation [3].

References:
[1] T. Giurgica-Tiron et al., “Digital zero noise extrapolation for quantum error mitigation”, https://arxiv.org/abs/2005.10921 <https://arxiv.org/abs/2005.10921>
[2] R. LaRose et al., “‘Mitiq: A software package for error mitigation on noisy quantum computers”, https://arxiv.org/abs/2009.04417 <https://arxiv.org/abs/2009.04417>. https://mitiq.readthedocs.io/<https://mitiq.readthedocs.io/>
[3] K. Temme et al., “Error mitigation for short-depth quantum circuits”, Phys. Rev. Lett. 119, 180509 (2017), https://arxiv.org/abs/1612.02058 <https://arxiv.org/abs/1612.02058>


We are also glad to announce two more seminars
more details in the next weeks — SAVE THE DATE(S)

Speaker: Patrick Potts (Lund University)
When: Thursday, 10th December 2020, 3PM (CET time)
Where: online (Zoom) zoom.us/my/aula.x
Title: Certifying nonclassical behavior for negative Keldysh
 quasiprobabilities

Speaker: Luca Razzoli (University of Modena & Reggio Emilia)
When: Thursday, 17th December 2020, 3PM (CET time)
Where: online (Zoom) zoom.us/my/aula.x
Title: Transport efficiency of continuous-time quantum walks on graphs

Speaker: Jan Chwedenczuk (Warsaw University)
When: Thursday, 7th January 2020, 3PM (CET time)
Where: online (Zoom) zoom.us/my/aula.x
Title: Many-body nonlocality as a resource for quantum-enhanced
metrology

Quantum Technology Lab – Dipartimento di Fisica – Università degli Studi di Milano