arXiv subjects

Martin Plesch

Publications and source records attributed to Martin Plesch.

At least 37 records · Page 2Linked to original sources

arXiv2021

Quantum key distribution overcoming extreme noise: simultaneous subspace coding using high-dimensional entanglement

High-dimensional entanglement promises to increase the information capacity of photons and is now routinely generated exploiting spatio-temporal degrees of freedom of single photons. A curious feature of these systems is the possibility to certify entanglement despite strong noise in the data. We show that it is also possible to exploit this noisy high-dimensional entanglement for quantum key distribution by introducing a protocol that uses mutliple subspaces of the high-dimensional system simultaneously. Our protocol can be used to establish a secret key even in extremely noisy experimental conditions, where qubit protocols fail. To show that, we analyze the performance of our protocol for noise models that apply to the two most commonly used sources of high-dimensional entanglement: time bins and spatial modes.

quant-ph↗

arXiv2019

The IYPT and the Ring Oiler Problem

The International Young Physicists' Tournament (IYPT) continued in 2018 in Beijing, China and 2019 in Warsaw, Poland with its 31\ts{st} and 32\ts{nd} editions. IYPT is a modern scientific competition for teams of high school students, also known as the Physics World Cup. It involves long time theoretical and experimental work focused on solving 17 publicly announced open ended problems in a teams of five. On top of that, teams have to present their solutions in front of other teams and scientific jury and get opposed and reviewed by their peers. Here we present a brief information about the competition with a specific focus on one of the IYPT 2018 tasks - the Ring Oiler. This seemingly simple mechanical problem appeared to be of such a complexity that even the dozens of participating teams and jurying scientists were not able to solve all of its subtleties.

physics.ed-ph↗

arXiv2019

Influence of Physical Properties of Hockey Stick Blade on Shots

Parameters of a shot of an ice hockey player are mostly determined by the capabilities of the player and the physical properties of the stick used. To reach better performance, every hockey player uses also a hockey tape for an adjustment of the stick blade, that changes both the damping properties as well as the friction coefficient of the blade surface. To show the unexpected extent to which these physical properties of the blade affect the shot, we compared two types of blade cover: traditional tape (rolled onto the blade) and a blade sticker that adheres to both sides of the hockey stick blade. We analysed high-speed recordings of two types of shots by 13 players, ranging from amateurs and junior players to NHL superstars. The two covers differ greatly in friction coefficient and stiffness, which results in significantly (more than $99\%$ confidence) greater speed, rotation and energy when using the stiffer and rougher sticker.

physics.pop-ph↗

arXiv2017

The International Young Physicists' Tournament 2017

In July 2017, National University of Singapore hosted the 30th International Young Physicists' Tournament (IYPT) with symbolic participation of $30$ competing teams. IYPT is a modern scientific competition for teams of high school students, also known as Physics World Cup. Here we present a brief report from this years competition with a concise list of problems solved by participating teams. For one of the problems, Torsion gyroscope, we also bring a glimpse into its theoretical and experimental solution.

physics.ed-ph↗

arXiv2017

Loss of Information in Quantum Guessing Game

Incompatibility of certain measurements -- impossibility of obtaining deterministic outcomes simultaneously -- is a well known property of quantum mechanics. This feature can be utilized in many contexts, ranging from Bell inequalities to device dependent QKD protocols. Typically, in these applications the measurements are chosen from a predetermined set based on a classical random variable. One can naturally ask, whether the non-determinism of the outcomes is due to intrinsic hiding property of quantum mechanics, or rather by the fact that classical, incoherent information entered the system via the choice of the measurement. Authors of [NJP 19, 023038 (2017)] examined this question for a specific case of two mutually unbiased measurements on systems of different dimensions. They have somewhat surprisingly shown that in case of qubits, if the measurements are chosen coherently with the use of a controlled unitary, outcomes of both measurements can be guessed deterministically. Here we extend their analysis and show that specifically for qubits, measurement result for any set of measurements with any a-priori probability distribution can be faithfully guessed by a suitable state preparation and measurement. We also show that up to a small set of specific cases, this is not possible for higher dimensions. This result manifests a deep difference in properties of qubits and higher dimensional systems and suggests that these systems might offer higher security in specific cryptographic protocols. More fundamentally, the results show that the impossibility of predicting a result of a measurement is not caused solely by a loss of coherence between the choice of the measurement and the guessing procedure.

quant-ph↗

arXiv2017

Gee-Haw Whammy Diddle

Gee-Haw Whammy Diddle is a seemingly simple mechanical toy consisting of a wooden stick and a second stick that is made up of a series of notches with a propeller at its end. When the wooden stick is pulled over the notches, the propeller starts to rotate. In spite of its simplicity, physical principles governing the motion of the stick and the propeller are rather complicated and interesting. Here we provide a thorough analysis of the system and parameters influencing the motion. We show that contrary to the results published on this topic so far, neither elliptic motion of the stick nor frequency synchronization is needed for starting the motion of the propeller.

physics.class-ph↗

arXiv2016

1-out-of-2 Oblivious transfer using flawed Bit-string quantum protocol

Oblivious transfer (OT) is an important tool in cryptography. It serves as a subroutine to other complex procedures of both theoretical and practical significance. Common attribute of OT protocols is that one party (Alice) has to send a message to another party (Bob) and has to stay oblivious on whether Bob did receive the message. Specific (OT) protocols vary by exact definition of the task - in the all-or-nothing protocol Alice sends a single bit-string message, which Bob is able to read only with 50% probability, whereas in 1-out-of-2 OT protocol Bob reads one out of two messages sent by Alice. These two flavours of protocol are known to be equivalent. Recently a computationally secure all-or-nothing OT protocol based on quantum states was developed in [A. Souto et. al., PRA 91, 042306], which however cannot be reduced to 1-out-of-2 OT protocol by standard means. Here we present an elaborated reduction of this protocol which retains the security of the original.

quant-ph↗

arXiv2016

Tight bound on the classical value of generalized Clauser-Horne-Shimony-Holt games

Non-local games are an important part of quantum information processing. Recently there has been an increased interest in generalizing non-local games beyond the basic setup by considering games with multiple parties and/or with large alphabet inputs and outputs. In this paper we consider another interesting generalization -- games with non-uniform inputs. Here we derive a tight upper bound for the classical winning probability for a specific family of non-local games with non-uniform input distribution, known as $\mathrm{CHSH}_q(p)$ which was introduced recently in the context of relativistic bit-commitment protocols by [Chakraborty et. al., PRL 115, 250501, 2015].

quant-ph↗

arXiv2015

An explicit classical strategy for winning a $\mathrm{CHSH}_{q}$ game

A $\mathrm{CHSH}_{q}$ game is a generalization of the standard two player $\mathrm{CHSH}$ game, having $q$ different input and output options. In contrast to the binary game, the best classical and quantum winning strategies are not known exactly. In this paper we provide a constructive classical strategy for winning a $\mathrm{CHSH}_{q}$ game, with $q$ being a prime. Our construction achieves a winning probability better than $\frac{1}{22}q^{-\frac{2}{3}}$, which is in contrast with the previously known constructive strategies achieving only the winning probability of $O(q^{-1})$.

quant-ph↗

arXiv2015

Device Independent Random Number Generation

Randomness is an invaluable resource in today's life with a broad use reaching from numerical simulations through randomized algorithms to cryptography. However, on the classical level no true randomness is available and even the use of simple quantum devices in a prepare-measure setting suffers from lack of stability and controllability. This gave rise to a group of quantum protocols that provide randomness certified by classical statistical tests -- Device Independent Quantum Random Number Generators. In this paper we review the most relevant results in this field, which allow the production of almost perfect randomness with help of quantum devices, supplemented with an arbitrary weak source of additional randomness. This is in fact the best one could hope for to achieve, as with no starting randomness (corresponding to no free will in a different concept) even a quantum world would have a fully deterministic description.

quant-ph↗

arXiv2014

Device-independent randomness amplification with a single device

Expansion and amplification of weak randomness with untrusted quantum devices has recently become a very fruitful topic of research. Here we contribute with a procedure for amplifying a single weak random source using tri-partite GHZ-type entangled states. If the quality of the source reaches a fixed threshold $R=\frac{1}{4}\log_{2}(10)$, perfect random bits can be produced. This technique can be used to extract randomness from sources that can't be extracted neither classically, nor by existing procedures developed for Santha-Vazirani sources. Our protocol works with a single fault-free device decomposable into three non-communicating parts, that is repeatedly reused throughout the amplification process.

quant-ph↗

arXiv2014

Device-independent randomness extraction for arbitrarily weak min-entropy source

Expansion and amplification of weak randomness plays a crucial role in many security protocols. Using quantum devices, such procedure is possible even without trusting the devices used, by utilizing correlations between outcomes of parts of the devices. We show here how to extract random bits with an arbitrarily low bias from a single arbitrarily weak min-entropy source in a device independent setting. To do this we use Mermin devices that exhibit super-classical correlations. Number of devices used scales polynomially in the length of the random sequence $n$. Our protocol is robust, it can tolerate devices that malfunction with a probability dropping polynomially in $n$ at the cost of a minor increase of the number of devices used.

quant-ph↗

arXiv2013

Comment on "Quantum Szilard Engine"

In a recently published letter [S. W. Kim, T. Sagawa, S. DeLiberato, and M. Ueda, PRL 106, 070401 (2011)] the influence of particle statistics on extractable work in the Szilard engine was discussed. We point out that the expressions given there suggest no work extraction is possible in the low temperature limit if more than two particles are used and thus are not optimal. We argue that the optimal extractable work is in general higher and in particular non-decreasing in the number of particles.

quant-ph↗

arXiv2012

Weak randomness completely trounces the security of QKD

In usual security proofs of quantum protocols the adversary (Eve) is expected to have full control over any quantum communication between any communicating parties (Alice and Bob). Eve is also expected to have full access to an authenticated classical channel between Alice and Bob. Unconditional security against any attack by Eve can be proved even in the realistic setting of device and channel imperfection. In this Letter we show that the security of QKD protocols is ruined if one allows Eve to possess a very limited access to the random sources used by Alice. Such knowledge should always be expected in realistic experimental conditions via different side channels.

quant-ph↗

arXiv2012

Measurement and Particle Statistics in the Szilard Engine

A Szilard Engine is a hypothetical device which is able to extract work from a single thermal reservoir by measuring the position of particles within the engine. We derive the amount of work that can be extracted from such a device in the low temperature limit. Interestingly, we show this work is determined by the information gain of the initial measurement rather than by the number and type of particles which constitute the working substance. Our work provides another clear connection between information gain and extractable work in thermodynamical processes.

quant-ph↗

arXiv2011

Purification of genuine multipartite entanglement

In tasks, where multipartite entanglement plays a central role, state purification is, due to inevitable noise, a crucial part of the procedure. We consider a scenario exploiting the multipartite entanglement in a straightforward multipartite purification algorithm and compare it to bipartite purification procedures combined with state teleportation. While complete purification requires an infinite amount of input states in both cases, we show that for an imperfect output fidelity the multipartite procedure exhibits a major advantage in terms of input states used.

quant-ph↗

arXiv2011

Quantum-state preparation with universal gate decompositions

In quantum computation every unitary operation can be decomposed into quantum circuits-a series of single-qubit rotations and a single type entangling two-qubit gates, such as controlled-NOT (CNOT) gates. Two measures are important when judging the complexity of the circuit: the total number of CNOT gates needed to implement it and the depth of the circuit, measured by the minimal number of computation steps needed to perform it. Here we give an explicit and simple quantum circuit scheme for preparation of arbitrary quantum states, which can directly utilize any decomposition scheme for arbitrary full quantum gates, thus connecting the two problems. Our circuit reduces the depth of the best currently known circuit by a factor of 2. It also reduces the total number of CNOT gates from 2^n to 23/24 2^n in the leading order for even number of qubits. Specifically, the scheme allows us to decrease the upper bound from 11 CNOT gates to 9 and the depth from 11 to 5 steps for four qubits. Our results are expected to help in designing and building small-scale quantum circuits using present technologies.

quant-ph↗

arXiv2010

Efficient compression of quantum information

We propose a scheme for an exact efficient transformation of a tensor product state of many identically prepared qubits into a state of a logarithmically small number of qubits. Using a quadratic number of elementary quantum gates we transform N identically prepared qubits into a state, which is nontrivial only on the first log(N+1) qubits. This procedure might be useful for quantum memories, as only a small portion of the original qubits has to be stored. Another possible application is in communicating a direction encoded in a set of quantum states, as the compressed state provides a high-effective method for such an encoding.

quant-ph↗