Showing papers on "No-teleportation theorem published in 2009"

Information causality as a physical principle

Abstract: Quantum physics has remarkable distinguishing characteristics. For example, it gives only probabilistic predictions (non-determinism) and does not allow copying of unknown states (no-cloning). Quantum correlations may be stronger than any classical ones, but information cannot be transmitted faster than light (no-signalling). However, these features do not uniquely define quantum physics. A broad class of theories exist that share such traits and allow even stronger (than quantum) correlations. Here we introduce the principle of 'information causality' and show that it is respected by classical and quantum physics but violated by all no-signalling theories with stronger than (the strongest) quantum correlations. The principle relates to the amount of information that an observer (Bob) can gain about a data set belonging to another observer (Alice), the contents of which are completely unknown to him. Using all his local resources (which may be correlated with her resources) and allowing classical communication from her, the amount of information that Bob can recover is bounded by the information volume (m) of the communication. Namely, if Alice communicates m bits to Bob, the total information obtainable by Bob cannot be greater than m. For m = 0, information causality reduces to the standard no-signalling principle. However, no-signalling theories with maximally strong correlations would allow Bob access to all the data in any m-bit subset of the whole data set held by Alice. If only one bit is sent by Alice (m = 1), this is tantamount to Bob's being able to access the value of any single bit of Alice's data (but not all of them). Information causality may therefore help to distinguish physical theories from non-physical ones. We suggest that information causality-a generalization of the no-signalling condition-might be one of the foundational properties of nature.

Are Random Pure States Useful for Quantum Computation

Abstract: We show the following: a randomly chosen pure state as a resource for measurement-based quantum computation is-with overwhelming probability-of no greater help to a polynomially bounded classical control computer, than a string of random bits. Thus, unlike the familiar "cluster states," the computing power of a classical control device is not increased from P to BQP (bounded-error, quantum polynomial time), but only to BPP (bounded-error, probabilistic polynomial time). The same holds if the task is to sample from a distribution rather than to perform a bounded-error computation. Furthermore, we show that our results can be extended to states with significantly less entanglement than random states.

Quantum teleportation scheme by selecting one of multiple output ports

Abstract: The scheme of quantum teleportation, where Bob has multiple $(N)$ output ports and obtains the teleported state by simply selecting one of the $N$ ports, is thoroughly studied. We consider both the deterministic version and probabilistic version of the teleportation scheme aiming to teleport an unknown state of a qubit. Moreover, we consider two cases for each version: (i) the state employed for the teleportation is fixed to a maximally entangled state and (ii) the state is also optimized as well as Alice's measurement. We analytically determine the optimal protocols for all the four cases and show the corresponding optimal fidelity or optimal success probability. All these protocols can achieve the perfect teleportation in the asymptotic limit of $N\ensuremath{\rightarrow}\ensuremath{\infty}$. The entanglement properties of the teleportation scheme are also discussed.

Quantum Teleportation via GHZ-like State

Abstract: We propose an efficient teleportation scheme for an unknown state to either one of two receivers via GHZ-like states. We also discuss the fidelity of the quantum state when the control party is uncooperative.

Super-Activation of Zero-Error Capacity of Noisy Quantum Channels

Abstract: We study various super-activation effects in the following zero-error communication scenario: One sender wants to send classical or quantum information through a noisy quantum channel to one receiver with zero probability of error. First we show that there are quantum channels of which a single use is not able to transmit classical information perfectly yet two uses can. This is achieved by employing entangled input states between different uses of the given channel and thus cannot happen for classical channels. Second we exhibit a class of quantum channel with vanishing zero-error classical capacity such that when a noiseless qubit channel or one ebit shared entanglement are available, it can be used to transmit $\log_2 d$ noiseless qubits, where 2d is the dimension of input state space. Third we further construct quantum channels with vanishing zero-error classical capacity when assisted with classical feedback can be used to transmit both classical and quantum information perfectly. These striking findings not only indicate both the zero-error quantum and classical capacities of quantum channels satisfy a strong super-additivity beyond any classical channels, but also highlight the activation power of auxiliary physical resources in zero-error communication.

Preparation of multi-atom specially entangled W-class state and splitting quantum information

Abstract: We give a protocol to prepare specially entangled W-class state of multi-atom which can be used to exactly teleport an arbitrarily unknown two-level two-atom state. During the process, the quantum information is split into n parts and the original quantum information can be sent to anyone of the n recipients with the other n-1 recipients’ collaboration. In addition, we will give a suggestion to realize this scheme via QED cavity.

Ultracold molecules: vehicles to scalable quantum information processing

Abstract: In this paper, we describe a novel scheme to implement scalable quantum information processing using Li–Cs molecular states to entangle 6Li and 133Cs ultracold atoms held in independent optical lattices. The 6Li atoms will act as quantum bits to store information and 133Cs atoms will serve as messenger bits that aid in quantum gate operations and mediate entanglement between distant qubit atoms. Each atomic species is held in a separate optical lattice and the atoms can be overlapped by translating the lattices with respect to each other. When the messenger and qubit atoms are overlapped, targeted single-spin operations and entangling operations can be performed by coupling the atomic states to a molecular state with radio-frequency pulses. By controlling the frequency and duration of the radio-frequency pulses, entanglement can be either created or swapped between a qubit messenger pair. We estimate operation fidelities for entangling two distant qubits and discuss scalability of this scheme and constraints on the optical lattice lasers. Finally we demonstrate experimental control of the optical potentials sufficient to translate atoms in the lattice.

Simpler criterion on W state for perfect quantum state splitting and quantum teleportation

Abstract: A simpler criterion is presented to judge whether a W state can be taken as quantum channel for perfectly splitting or teleporting an arbitrary single-qubit state. If the W state is usable, the detailed manipulations in the two quantum information processes are amply shown. Moreover, some relevant discussions are made.

Threshold multiparty quantum-information splitting via quantum channel encryption

Abstract: We propose a (t, n)-threshold multiparty quantum-information splitting protocol following some ideas of the standard teleportation protocol [C. H. Bennett, G. Brassard, C. Crpeau, R. Jozsa, A. Peres and W. K. Wootters, Phys. Rev. Lett.70 (1993) 1895] and Tokunaga et al.'s protocol [Y. Tokunaga, T. Okamoto and N. Imoto, Phys. Rev. A71 (2005) 012314]. The sender distributes the classical shared keys to his or her n agents and each agent owns a secret key in advance. The sender's quantum information can be extracted by an agent subset by collaboration in such a way that at least t or more agents can get the quantum information with the mutual assistances but any t - 1 or fewer agents cannot. In contrast to the previous multiparty quantum-information splitting protocols in which the sender's quantum information can be recovered only if all the agents collaborate, our protocol is more practical and more flexible.

Quantum Cryptography Based Solely on Bell's Theorem

Abstract: Information-theoretic key agreement is impossible to achieve from scratch and must be based on some - ultimately physical - premise. In 2005, Barrett, Hardy, and Kent showed that unconditional security can be obtained in principle based on the impossibility of faster-than-light signaling; however, their protocol is inefficient and cannot tolerate any noise. While their key-distribution scheme uses quantum entanglement, its security only relies on the impossibility of superluminal signaling, rather than the correctness and completeness of quantum theory. In particular, the resulting security is device independent. Here we introduce a new protocol which is efficient in terms of both classical and quantum communication, and that can tolerate noise in the quantum channel. We prove that it offers device-independent security under the sole assumption that certain non-signaling conditions are satisfied. Our main insight is that the XOR of a number of bits that are partially secret according to the non-signaling conditions turns out to be highly secret. Note that similar statements have been well-known in classical contexts. Earlier results had indicated that amplification of such non-signaling-based privacy is impossible to achieve if the non-signaling condition only holds between events on Alice's and Bob's sides. Here, we show that the situation changes completely if such a separation is given within each of the laboratories.

Superactivation of the Asymptotic Zero-Error Classical Capacity of a Quantum Channel

Abstract: The zero-error classical capacity of a quantum channel is the asymptotic rate at which it can be used to send classical bits perfectly, so that they can be decoded with zero probability of error. We show that there exist pairs of quantum channels, neither of which individually have any zero-error capacity whatsoever (even if arbitrarily many uses of the channels are available), but such that access to even a single copy of both channels allows classical information to be sent perfectly reliably. In other words, we prove that the zero-error classical capacity can be superactivated. This result is the first example of superactivation of a classical capacity of a quantum channel.

Perfect state transfer without state initialization and remote collaboration

Abstract: We present a perfect state transfer protocol via a qubit chain with the evolution governed by the $xx$ Hamiltonian. In contrast to the recent protocol announced in Phys. Rev. Lett. 101, 230502 (2008), our method does not demand any remote-cooperated initialization and sending classical information about measurement outcomes. We achieve the perfect state transfer only with the assumption of access to two spins at each end of the chain, while the initial state of the whole chain is irrelevant.

Adaptive quantum teleportation

Abstract: We consider multiple teleportation in the Knill-Laflamme-Milburn (KLM) scheme. We introduce adaptive teleportation, i.e., such that the choice of entangled state used in the next teleportation depends on the results of the measurements performed during the previous teleportations. We show that adaptive teleportation enables an increase in the probability of faithful multiple teleportation in the KLM scheme. In particular if a qubit is to be teleported more than once then it is better to use nonmaximally entangled states than maximally entangled ones in order to achieve the highest probability of faithful teleportation.

Quantum Information and the PCP Theorem

Abstract: Our main result is that the membership x∈SAT (for x of length n) can be proved by a logarithmic-size quantum state |Ψ〉, together with a polynomial-size classical proof consisting of blocks of length polylog(n) bits each, such that after measuring the state |Ψ〉 the verifier only needs to read one block of the classical proof. This shows that if a short quantum witness is available then a (classical) PCP with only one query is possible. Our second result is that the class QIP/qpoly contains all languages. That is, for any language L (even non-recursive), the membership x∈L (for x of length n) can be proved by a polynomial-size quantum interactive proof, where the verifier is a polynomial-size quantum circuit with working space initiated with some quantum state |Ψ L,n 〉 (depending only on L and n). Moreover, the interactive proof that we give is of only one round, and the messages communicated are classical. The advice |Ψ L,n 〉 given to the verifier can also be replaced by a classical probabilistic advice, as long as this advice is kept as a secret from the prover. Our result can hence be interpreted as: the class IP/rpoly contains all languages. For the proof of the second result, we introduce the quantum low-degree-extension of a string of bits. The main result requires an additional machinery of quantum low-degree-test.

Economic and Deterministic Quantum Teleportation of Arbitrary Bipartite Pure and Mixed State with Shared Cluster Entanglement

Abstract: We present a novel protocol for teleportation of arbitrary bipartite pure and mixed state with shared cluster entanglement in this paper. By employing Bell-state measurement on the teleported state and the shared cluster state twice, a sender could transmit the arbitrary bipartite state to a distant receiver. We show the good feature of the cluster state channel, with which it can realize the deterministic teleportation rather than probabilistic one. Moreover, since we require less particles to be shared and need no auxiliary qubit in our protocol, it is more efficient and applicable than the previous schemes.

Lower bound on the communication cost of simulating bipartite quantum correlations

Abstract: Suppose Alice and Bob share a maximally entangled state of any finite dimension and each perform two-outcome measurements on the respective part of the state. It is known, due to the recent result of Regev and Toner, that if a classical model is augmented with two bits of communication, then all the quantum correlations arising from these measurements can be reproduced. Here, we show that two bits of communication are in fact necessary for the perfect simulation. In particular, we prove that a pair of maximally entangled four-dimensional quantum systems cannot be simulated by a classical model augmented by only one bit of communication.

Quantum Key Distribution Using Vacuum-One-Photon Qubits: Maximum Number of Transferable Bits per Particle

Abstract: Quantum key distribution schemes which employ encoding on vacuum-one-photon qubits are capable of transferring more information bits per particle than the standard schemes employing polarization or phase coding. We calculate the maximum number of classical bits per particle that can be securely transferred when the key distribution is performed with the BB84 and B92 protocols, respectively, using the vacuum-one-photon qubits. In particular, we show that for a generalized B92 protocol with the vacuum-one-photon qubits, a maximum of two bits per particle can be securely transferred. We also demonstrate the advantage brought about by performing a generalized measurement that is optimized for unambiguous discrimination of the encoded states: the parameter range where the transfer of two bits per particle can be achieved is dramatically enhanced as compared to the corresponding parameter range of projective measurements.

Minimal classical communication and measurement complexity for quantum information splitting of a two-qubit state

Abstract: We investigate the usefulness of the highly entangled five-partite cluster and Brown states for the quantum information splitting (QIS) of a special kind of two-qubit state using remote state preparation. In our schemes, the information that is to be shared is known to the sender. We show that, QIS can be accomplished with just two classical bits, as opposed to four classical bits, when the information that is to be shared is unknown to the sender. The present algorithm, demonstrated through the cluster and Brown states is deterministic as compared to the previous works in which it was probabilistic.

Quantum information theory: The bits don't add up

Abstract: A counterexample to the 'additivity question', the most celebrated open problem in the mathematical theory of quantum information, casts doubt on the possibility of finding a simple expression for the information capacity of a quantum channel.

The impact of classical electronics constraints on a solid-state logical qubit memory

Abstract: We describe a fault-tolerant memory for an error-corrected logical qubit based on silicondouble quantum dot physical qubits. Our design accounts for constraints imposed by supportingclassical electronics. A signi cant consequence of the constraints is to add error-prone idle stepsfor the physical qubits. Even using a schedule with provably minimum idle time, for our noisemodel and choice of error-correction code, we nd that these additional idles negate any bene tsof error correction. Using additional qubit operations, we can greatly suppress idle-inducederrors, making error correction bene cial, provided the qubit operations achieve an error rateless than 2 10 5 . We discuss other consequences of these constraints such as error-correctioncode choice and physical qubit operation speed. While our analysis is speci c to this memoryarchitecture, the methods we develop are general enough to apply to other architectures as well.1 Introduction Quantum information processing (QIP) promises a path towards resolving currently computationally-intractable problems [1]. However, quantum bits (qubits) used for storing quantum information are,unfortunately, much more susceptible to errors than classical bits. Realization of error-correctedquantum computation, therefore, represents a critical QIP engineering pursuit. A key concept inthis pursuit is the redundant encoding of a logical qubit in the state of many physical qubits. Thisredundancy allows one to check for errors and correct them.This paper presents a solid-state architecture for a single logical qubit memory that accountsfor the constraints imposed by both classical electronics and the native quantum gate set|the available set of qubit transformations the solid-state system provides. Quantum-computingarchitectures have been considered previously, for example in ion traps [2] and solid-state [3,4].These analyses began the study of incorporating realistic implementation constraints. We extendthese studies in the solid-state to include explicit electronic constraints, where we expect electronicsintegration to be easier and the least constrained. From this we have gained a number of critical

Long-distance quantum teleportation assisted with free-space entanglement distribution ∗

Abstract: Faithful long-distance quantum teleportation necessitates prior entanglement distribution between two communicated locations. The particle carrying on the unknown quantum information is then combined with one particle of the entangled states for Bell-state measurements, which leads to a transfer of the original quantum information onto the other particle of the entangled states. However in most of the implemented teleportation experiments nowadays, the Bell-state measurements are performed even before successful distribution of entanglement. This leads to an instant collapse of the quantum state for the transmitted particle, which is actually a single-particle transmission thereafter. Thus the true distance for quantum teleportation is, in fact, only in a level of meters. In the present experiment we design a novel scheme which has overcome this limit by utilizing fiber as quantum memory. A complete quantum teleportation is achieved upon successful entanglement distribution over 967 meters in public free space. Active feed-forward control techniques are developed for real-time transfer of quantum information. The overall experimental fidelities for teleported states are better than 89.6%, which signify high-quality teleportation.

Methods of Constructing Quantum Channels for Teleporting a General Two-qubit State

Abstract: By resorting to the tensor analysis, we derived an explicit CPM (channel parameter matrix) criterion based on the Bell state measurements. This criterion can be used to judge whether a four-qubit state can be employed as quantum channel or not for teleporting a general two-qubit state. According to this criterion, we presented a variety of quantum channels for faithful and deterministic teleportation of a general two-qubit state, which can provide more flexible choices for the experimenters.

Can classical noise enhance quantum transmission

Abstract: A modified quantum teleportation protocol broadens the scope of the classical forbidden-interval theorems for stochastic resonance. The fidelity measures performance of quantum communication. The sender encodes the two classical bits for quantum teleportation as weak bipolar subthreshold signals and sends them over a noisy classical channel. Two forbidden-interval theorems provide a necessary and sufficient condition for the occurrence of the nonmonotone stochastic resonance effect in the fidelity of quantum teleportation. The condition is that the noise mean must fall outside a forbidden interval related to the detection threshold and signal value. An optimal amount of classical noise benefits quantum communication when the sender transmits weak signals, the receiver detects with a high threshold and the noise mean lies outside the forbidden interval. Theorems and simulations demonstrate that both finite-variance and infinite-variance noise benefit the fidelity of quantum teleportation.

Teleportation of an Arbitrary Two-Particle State via a Single Cluster-Class State

Abstract: Teleportation of an arbitrary two-qubit state with a single partially entangled state, a four-qubit linear cluster-class state, is studied. The case is more practical than previous ones using maximally entangled states as the quantum channel. In order to realize teleportation, we first construct a cluster-basis of 16 orthonormal cluster states. We show that quantum teleportation can be successfully implemented with a certain probability if the receiver can adopt appropriate unitary transformations after receiving the sender's cluster-basis measurement information. In addition, an important conclusion can be obtained that a four-qubit maximally entangled state (cluster state) can be extracted from a single copy of the cluster-class state with the same probability as the teleportation in principle.

Quantum Teleportation with an Accelerated Observer and Black Hole Information

Abstract: Nonperturbative analysis of quantum entanglement and quantum teleportation protocol using oscillator variables carried by observers in relativistic motion under the continuous influence of the environment is given. The full time evolution of quantum entanglement among static and accelerated observers is studied. The environment plays a dual role. While it creates bipartite and tripartite entanglement among observers even when the initial state is separable, it suppresses the entanglement via decoherence. Motivated by the black hole information problem, we consider quantum teleportation between static and accelerated observers. Acceleration of the observer suppresses fidelity of teleportation. Some of the quantum information escapes outside of the horizon in the form of bipartite and tripartite entanglement during the teleportation process. Explicit calculation of information loss is provided. In addition to the loss due to the interaction with the environment, there is an intrinsic loss originated in a measurement process. We discuss the implications of our results on the black hole case.

PERFECT TELEPORTATION OF UNKNOWN QUDIT BY A d-LEVEL GHZ CHANNEL

Abstract: In the past decades, various schemes of teleportation of quantum states through different types of quantum channels (a prior shared entangled state between the sender and the receiver), e.g. EPR pairs, generalized Bell states, qubit GHZ states, standard W states and its variations, genuine multiqubit entanglement states, etc., have been developed. Recently, three-qutrit quantum states and two-qudit quantum states have also been considered as quantum channels for teleportation. In this paper, we investigate the teleportation of an unknown qudit using a d level GHZ state, i.e. a three-qudit maximally entangled state, as quantum channel. We design a general scheme of faithful teleportation of an unknown qudit using a d-level GHZ state shared between the sender and the receiver, or among the sender, the receiver and the controller; an unknown two-qudit of Schmidt form using a d level GHZ state shared between the sender and the receiver; as well as an unknown arbitrary two-qudit using two shared d level GHZ states between the sender, the receiver and the controller, or using one shared d level GHZ state and one shared generalized Bell state. We obtain the general formulas of Alice's measurement basis, Charlie's measurement basis and Bob's unitary operations to recover the input state of Alice. It is intuitionistic to generalize the protocols of teleporting an arbitrary two-qudit state to teleporting an arbitrary n-qudit state.

Quantum Algorithms Know in Advance 50% of the Solution They Will Find in the Future

Abstract: Quantum algorithms require less operations than classical algorithms. The exact reason of this has not been pinpointed until now. Our explanation is that quantum algorithms know in advance 50% of the solution of the problem they will find in the future. In fact they can be represented as the sum of all the possible histories of a respective “advanced information classical algorithm”. This algorithm, given the advanced information (50% of the bits encoding the problem solution), performs the operations (oracle’s queries) still required to identify the solution. Each history corresponds to a possible way of getting the advanced information and a possible result of computing the missing information. This explanation of the quantum speed up has an immediate practical consequence: the speed up comes from comparing two classical algorithms, with and without advanced information, with no physics involved. This simplification could open the way to a systematic exploration of the possibilities of speed up.

Transformation matrix of network-controlled teleportation

Abstract: According to the collapse principle of quantum state when being measured, we present a method of directly writing out transformation matrix by looking at the figure of a network-controlled quantum channel. We find the rule of constructing transformation matrix in network-controlled teleportation. Based on this method, we gain transformation matrix of two-qubit state teleportation in which two GHZ state act as controlled quantum channels. We further proposed a scheme of one-qubit teleportation by a series-controlled quantum channel and teleportation of three-qubit via a typical network controlled quantum channel, in which two-qubit state instead of GHZ state act as quantum channel. So, Hadamard operation is not necessary in our scheme.