Shubhayan Sarkar

Université Libre de Bruxelles | ULB · Department of Physics

Entanglement and nonlocality are key resources for most of the quantum information protocols. It is well-established now that every entangled state is nonlocal with respect to semi-quantum games. However, there is a lack of witnesses that can used to observe any form of nonlocality of every entangled state. In this work, we focus on the swap-steeri...

In any known description of nature, two physical systems are considered independent of each other if any action on one of the systems does not change the other system. From our classical intuitions about the world, we further conclude that these two systems are not affecting each other in any possible way, and thus these two systems are causally di...

Quantum steering is an asymmetric form of quantum nonlocality where one can trust the measurements of one of the parties. In this work, inspired by practical considerations, we investigate the scenario in which one cannot fully trust their measurement devices, just up to some level of precision. We first find the effect of such an imprecision on st...

Mathematica code for evaluating the tight corrected local bound for the simplest quantum steering scenario (n=m=d=2) with distrust [See https://arxiv.org/abs/2308.15337]. The algorithm can be generalised to arbitrary steering scenarios.

Quantum steering is an asymmetric form of quantum nonlocality where one can trust the measurements of one of the parties. In this work, inspired by practical considerations we investigate the scenario if one can not fully trust their measurement devices but only up to some precision. We first find the effect of such an imprecision on standard devic...

The security of any cryptographic scheme relies on access to random number generators. Device-independently certified random number generators provide maximum security as one can discard the presence of an intruder by considering only the statistics generated by these devices. Any of the known device-independent schemes to certify randomness requir...

Quantum networks with independent sources allow the observation of quantum nonlocality without inputs. Consequently, the incompatibility of measurements is not a necessity for observing quantum nonlocality when one has access to independent sources. Here we investigate the minimal scenario without inputs where one can observe any form of quantum no...

Random number generators play an essential role in cryptography and key distribution. It is thus important to verify whether the random numbers generated from these devices are genuine and unpredictable by any adversary. Recently, quantum nonlocality has been identified as a resource that can be utilised to certify randomness. Although these scheme...

One of the basic observations of the classical world is that physical entities are real and can be distinguished from each other. However, within quantum theory, the idea of physical realism is not well established. A framework to analyse how observations in experiments can be described using some physical states of reality was recently developed,...

Certification of quantum systems and their properties has become a field of intensive study. Here, taking advantage of the one-sided device-independent (1SDI) scenario (also known as the quantum steering scenario), we propose a self-testing scheme for all bipartite entangled states using a single family of steering inequalities with the minimal num...

In recent times, device-independent certification of quantum states has been one of the intensively studied areas in quantum information. However, all such schemes utilize projective measurements which are practically difficult to generate. In this paper, we consider the one-sided device-independent scenario and propose a self-testing scheme for th...

Exploiting the tension between the two dynamics of quantum theory (QT) in the Wigner's Friend thought experiment, we point out that the standard QT leads to inconsistency in observed probabilities of measurement outcomes between two superobservers: Wigner and his Student. To avoid such inconsistent predictions of QT, we hypothesize two distinct per...

The emergence of quantum theory at the beginning of 20−th century has changed our view of the microscopic world and has led to applications such as quantum teleportation, quantum random number generation and quantum computation to name a few, that could never have been realised using classical systems. One such application that has attracted consid...

The emergence of quantum theory at the beginning of 20$-th$ century has changed our view of the microscopic world and has led to applications such as quantum teleportation, quantum random number generation and quantum computation to name a few, that could never have been realised using classical systems. One such application that has attracted cons...

Within the quantum networks scenario, we introduce a single scheme allowing to certify three different types of composite projective measurements acting on a three-qubit Hilbert space: one constructed from genuinely entangled GHZ-like states, one constructed from fully product vectors that exhibit the phenomenon of nonlocality without entanglement...

In recent times, device-independent certification of quantum states has been one of the intensively studied areas in quantum information. However, all such schemes utilise projective measurements which are practically difficult to generate. In this work, we consider the one-sided device-independent (1SDI) scenario, and propose a self-testing scheme...

In this Letter we consider the problem of the certification of quantum measurements with an arbitrary number of outcomes. We propose a simple scheme for certifying any set of d-outcome projective measurements which do not share any common invariant proper subspace, termed here genuinely incompatible, and the maximally entangled state of two qudits....

Device-independent certification schemes have gained a lot of interest lately, not only for their applications in quantum information tasks, but also their implications towards foundations of quantum theory. The strongest form of device-independent certification, known as self-testing, often requires for a Bell inequality to be maximally violated b...

While it has recently been demonstrated how to certify the maximal amount of randomness from any pure two-qubit entangled state in a device-independent way, the problem of optimal randomness certification from entangled states of higher local dimension remains open. Here we introduce a method for device-independent certification of the maximal poss...

While it has recently been demonstrated how to certify the maximal amount of randomness from any pure two-qubit entangled state in a device-independent way [E. Woodhead et al., Phys. Rev. Research 2, 042028(R)(2020)], the problem of optimal randomness certification from entangled states of higher local dimension remains open. Here we introduce a me...

Device independent certification schemes have gained a lot of interest lately, not only for their applications in quantum information tasks but also their implications towards foundations of quantum theory. The strongest form of device independent certification, known as self-testing, often requires for a Bell inequality to be maximally violated by...

Certification of quantum systems and their properties has become an intensively studied field in quantum information, leading to several important applications, one of them being the certification of genuine randomness. Here we propose a self-testing scheme for all bipartite entangled states using a single family of steering inequalities with the m...

Bell nonlocality as a resource for device-independent certification schemes has been studied extensively in recent years. The strongest form of device-independent certification is referred to as self-testing, which given a device, certifies the promised quantum state as well as quantum measurements performed on it without any knowledge of the inter...

Exploiting the tension between the two dynamics of quantum theory (QT) or the so-called "measurement problem" of QT within a modified version of Wigner's Friend thought experiment, we point out that two different descriptions of Friend's lab by two different observers, Wigner and his Student, applying the same textbook QT can lead to inconsistency...

In recent years nonlocality has been extensively explored as a resource for self-testing -- a device-independent way of certification of entangled quantum states and measurements performed on them. However, most of the efforts in designing self-testing schemes were concerned with entangled quantum states, leaving the problem of certification of qua...

Existence of physical reality in the classical world is a well-established fact from day-to-day observations. However within quantum theory, it is not straightforward to reach such a conclusion. A framework to analyse how observations can be described using some physical states of reality in a theory independent way was recently developed, known as...

We propose a one-sided device-independent protocol for certification of any set of d-outcome projective measurements that are “genuinely incompatible measurements” meaning that they do not share any invariant subspace including mutually unbiased bases.

Predicting how cooperative behavior arises in the thermodynamic limit is one of the outstanding problems in evolutionary game theory. For two player games, cooperation is seldom the Nash equilibrium. However, in the thermodynamic limit cooperation is the natural recourse regardless of whether we are dealing with humans or animals. In this work, we...

Bell nonlocality as a resource for device independent certification schemes has been studied extensively in recent years. The strongest form of device independent certification is referred to as self-testing, which given a device certifies the promised quantum state as well as quantum measurements performed on it without any knowledge of the intern...

In this work, we aim to answer the question- what triggers cooperative behaviour in the thermodynamic limit by taking recourse to the Public goods game. Using the idea of mapping the Ising model Hamiltonian to payoffs in game theory we calculate the Magnetisation of a game in the thermodynamic limit. We see a phase transition in the thermodynamic l...

The free rider problem is one of the most well studied problems in economics. The solution proposed mainly is punitive in order to deter people from free riding. In this work we introduce quantum strategies and also study the problem by using the mathematical structure of 1D Ising model in the infinite player limit. We observe that for maximum enta...

The quantum Nash equilibrium in the thermodynamic limit is studied for games like quantum Prisoner's dilemma and quantum game of Chicken. A phase transition is seen in both games as function of the entanglement in the game. We observe that for maximal entanglement irrespective of the classical payoffs, majority of players choose quantum strategy ov...

How does cooperative behavior emerge in the thermodynamic limit is one of the sought after problems in evolutionary game theory. There have been previous attempts to understand how cooperation emerges in the thermodynamic limit even when defection is the Nash equilibrium in the two player game. However, we find that a particular method of Adami and...

The free rider problem is one of the most well studied problems in economics. The solution proposed mainly is punitive in order to deter people from free riding. In this work we introduce quantum strategies and also study the problem in the thermodynamic limit by drawing analogies with the 1D Ising model. We observe that for maximum entanglement, i...

Quantum teleportation of an unknown quantum state is one of the few communication tasks which has no classical counterpart. Usually the aim of teleportation is to send an unknown quantum state to a receiver. But is it possible in some way that the receiver’s state has more quantum discord than the sender’s state? We look at a scenario where Alice a...

The quantum Nash equilibrium in the thermodynamic limit is studied for games like quantum Prisoner's dilemma and the quantum game of chicken. A phase transition is seen in both games as a function of the entanglement in the game. We observe that for maximal entanglement irrespective of the classical payoffs, a majority of players choose Quantum str...

Quantum information-theoretic approach has been identified as a way to understand the foundations of quantum mechanics as early as 1950 due to Shannon. However there hasn’t been enough advancement or rigorous development of the subject. In the following paper we try to find relationship between a general quantum mechanical observable and von Neuman...