Ultra-large-scale continuous-variable cluster states multiplexed in the time domain

Abstract

Quantum computers promise ultrafast performance of certain tasks 1 . Experimentally appealing, measurement-based quantum computation (MBQC) 2 requires an entangled resource called a cluster state 3 , with long computations requiring large cluster states. Previously, the largest cluster state consisted of 8 photonic qubits 4 or light modes 5 , while the largest multipartite entangled state of any sort involved 14 trapped ions 6 . These implementations involve quantum entities separated in space, and in general, each experimental apparatus is used only once. Here, we circumvent this inherent inefficiency by multiplexing light modes in the time domain. We deterministically generate and fully characterise a continuous-variable cluster state 7,8 containing more than 10,000 entangled modes. This is, by 3 orders of magnitude, the largest entangled state ever created to date. The entangled modes are individually addressable wavepackets of light in two beams. Furthermore, we present an efficient scheme for MBQC on this cluster state based on sequential applications of quantum teleportation.Originally formulated as a demonstration as to why quantum mechanics must be incomplete in the famous 1935 Einstein-Podolsky-Rosen (EPR) paradox 9 , entanglement is now recognized as a signature feature of quantum physics 10 , and it plays a central role in various quantum information processing (QIP) protocols 1,11 . For example, the bipartite entangled state known as an EPR state 9 is a resource for quantum teleportation (QT), whereby a quantum state is transferred from one location to another without physical transfer of the quantum information 12-14 .Measurement-based quantum computation (MBQC) 2,7,8,[15][16][17][18] , which is based on the QT of information and logic gates, requires the special class of multipartite entangled resource states known as cluster states 3 . The number of entangled quantum entities and their entanglement structure (represented by a graph) determines the resource space available for computation.Ultra-large-scale QIP (which could be based on MBQC) will require ultra-large-scale entangled 2 states 2,7,8 .In the vast majority of optical experiments, quantum modes are distinguished from each other by their spatial location. This leads to an inherent lack of scalability as each additional entangled party requires an increase in laboratory equipment and dramatically increases the complexity of the optical network 19,20 . Further, due to the probabilistic nature of photon pair generation, demonstrations involving the postselection of photonic qubits 4,15,16 suffer from dramatically reduced event success rates with each additional qubit.One method to overcome this problem of scalability is to deterministically encode the modes within one beam. Entanglement between quadrature-phase amplitudes in continuouswave laser beams has been deterministically created and exploited in QIP 5,13,14,[17][18][19][21][22][23] , even though the quantum correlations are finite. Previous attempts to deterministically create cluster ...

Physics: Unite to build a quantum Internet

“…Cluster states that link thousands of nodes have already been created in the laboratory 9 . The challenges are to demonstrate how they might be deployed over long distances, as well as how to store quantum states at the nodes and update them constantly using quantum codes.…”

Systematic construction of genuine-multipartite-entanglement criteria in continuous-variable systems using uncertainty relations

“…+p n [31]. It is worth noting that these type of unnormalised eigenstates are well approximated by squeezed multipartite gaussian states that have been generated in several experiments recently [12][13][14]. In the next section we use this type of commuting non-local linear operators to derive criteria that are useful to detect genuine multipartite entanglement in any n-partite state.…”

“…For example, we can not use the UR in Eq. (12) to set the functional F and the function f in our PPT-URNLO genuine entanglement criterion in Eq. (28).…”

Measurement-Based Quantum Computation with Trapped Ions

“…Scaling up the non-deterministic methods used to generate entangled states in these works is very challenging, since their success probably reduces exponentially in photon number. Very recently there has been work on generating cluster states in continuous variables of light fields [13].In this work we present the first demonstration of MBQC using trapped ions. Furthermore, we make two experimental steps forward in the model of MBQC that are systemindependent: the deterministic generation of cluster states and the demonstration of quantum error correction (QEC).…”

“…Scaling up the non-deterministic methods used to generate entangled states in these works is very challenging, since their success probably reduces exponentially in photon number. Very recently there has been work on generating cluster states in continuous variables of light fields [13].…”