Encoding classical information in gauge subsystems of quantum codes

In this paper, we show how to construct hybrid quantum-classical codes from subsystem codes by encoding the classical information into the gauge qudits using gauge fixing. Unlike previous work on hybrid codes, we allow for two separate minimum distances, one for the quantum information and one for the classical information. We give an explicit construction of hybrid codes from two classical linear codes using Bacon–Casaccino subsystem codes, as well as several new examples of good hybrid code.

Stronger correlations than dense coding with the same quantum resources

Dense coding is the seminal example of how entanglement can boost quantum communication. By sharing an Einstein-Podolsky-Rosen (EPR) pair, dense coding allows one to transmit two bits of classical information while sending only a single qubit [1]. This doubling of the channel capacity is the largest allowed in quantum theory [2]. In this letter we show in both theory and experiment that same elementary resources, namely a shared EPR pair and qubit communication, are strictly more powerful than two classical bits in more general communication tasks. In contrast to dense coding experiments [3–8], we show that these advantages can be revealed using merely standard optical Bell state analysers [9, 10]. Our results reveal that the power of entanglement in enhancing quantum communications qualitatively goes beyond boosting channel capacities.

Thermality Versus Objectivity: Can They Peacefully Coexist?

Under the influence of external environments, quantum systems can undergo various different processes, including decoherence and equilibration. We observe that macroscopic objects are both objective and thermal, thus leading to the expectation that both objectivity and thermalisation can peacefully coexist on the quantum regime too. Crucially, however, objectivity relies on distributed classical information that could conflict with thermalisation. Here, we examine the overlap between thermal and objective states. We find that in general, one cannot exist when the other is present. However, there are certain regimes where thermality and objectivity are more likely to coexist: in the high temperature limit, at the non-degenerate low temperature limit, and when the environment is large. This is consistent with our experiences that everyday-sized objects can be both thermal and objective.

PRACTICAL UTILITY OF SAMSARJANA KRAMA: A REVIEW

The Shodhana procedures are mainly divided into three phases known as Trividha Karma. Acharya Dalhana has clarified Trividha Karma in the context of Shodhana as Poorva Karma, Pradhana Karma and Paschat Karma. Samsarjana Krama is a special diet pattern which is followed as Paschat Karma after Samshodhana. After Samshodhana Karma the Atura Shareera will have reduced tolerance owing to the elimination of large quantities of Dosha and Mala from the body, leading to weakness and reduction in digestive fire. This can be corrected only by following proper Samsarjana Krama with respect to the Shuddhi attained by the Atura. Acharyas detailed the Samsarjana Krama for two Annakala with respect to the ancient time period in contrast to the present scenario, where we are following three Annakala. To get a successful result from the treatment the patient should follow all the 3 stages properly. Hence, here an attempt is made to modify the Samsarjana Krama chart for the present era with respect to classical information given by the Acharyas.

Emergent classicality in general multipartite states and channels

In a quantum measurement process, classical information about the measured system spreads throughout the environment. Meanwhile, quantum information about the system becomes inaccessible to local observers. Here we prove a result about quantum channels indicating that an aspect of this phenomenon is completely general. We show that for any evolution of the system and environment, for everywhere in the environment excluding an O(1)-sized region we call the "quantum Markov blanket," any locally accessible information about the system must be approximately classical, i.e. obtainable from some fixed measurement. The result strengthens the earlier result of Brandão et al. (Nat. comm. 6:7908) in which the excluded region was allowed to grow with total environment size. It may also be seen as a new consequence of the principles of no-cloning or monogamy of entanglement. Our proof offers a constructive optimization procedure for determining the "quantum Markov blanket" region, as well as the effective measurement induced by the evolution. Alternatively, under channel-state duality, our result characterizes the marginals of multipartite states.

Beyond IIT: (how) can we model the evolution of consciousness?

Tononi et al.'s "integrated information theory" (IIT) postulates rules for assigning measures Phi and qualia types Q of consciousness to classical information networks. We consider whether IIT is compatible with Darwinian evolution. We argue that an IIT-like theory that assigns consciousness to physical systems by relatively simple mathematical rules poses extraordinary ?ne-tuning problems.For example, why, among all possible lawlike theories of consciousness, do we have one that makes us conscious of a high-level narrative of our environment and actions, so accurate that it appears to us to cause our behaviour?We introduce IIT+, a class of extensions of IIT in which Phi and/or Q influence the network dynamics. We argue that IIT+-like theories, unlike IIT-like theories, offer at least partial explanations of how some key features of consciousness evolved. We conclude that if one takes seriously Darwinian evolution and the case for an IIT-like theory, one has to take seriously the case for an IIT+-like theory.

Quantum information as the information of infinite collections or series

The quantum information introduced by quantum mechanics is equivalent to a certain generalization of classical information: from finite to infinite series or collections. The quantity of information is the quantity of choices measured in the units of elementary choice. The “qubit”, can be interpreted as that generalization of “bit”, which is a choice among a continuum of alternatives. The axiom of choice is necessary for quantum information. The coherent state is transformed into a well-ordered series of results in time after measurement. The quantity of quantum information is the transfinite ordinal number corresponding to the infinity series in question. The transfinite ordinal numbers can be defined as ambiguously corresponding “transfinite natural numbers” generalizing the natural numbers of Peano arithmetic to “Hilbert arithmetic” allowing for the unification of the foundations of mathematics and quantum mechanics.

Poisson Quantum Information

By taking a Poisson limit for a sequence of rare quantum objects, I derive simple formulas for the Uhlmann fidelity, the quantum Chernoff quantity, the relative entropy, and the Helstrom information. I also present analogous formulas in classical information theory for a Poisson model. An operator called the intensity operator emerges as the central quantity in the formalism to describe Poisson states. It behaves like a density operator but is unnormalized. The formulas in terms of the intensity operators not only resemble the general formulas in terms of the density operators, but also coincide with some existing definitions of divergences between unnormalized positive-semidefinite matrices. Furthermore, I show that the effects of certain channels on Poisson states can be described by simple maps for the intensity operators.