We consider imperfect two-mode bosonic quantum transducers that cannot

completely transfer an initial source-system quantum state due to insufficient

coupling strength or other non-idealities. We show that such transducers can

generically be made perfect by using interference and phase-sensitive

amplification. Our approach is based on the realization that a particular kind

of imperfect transducer (one which implements a swapped quantum non-demolition

(QND) gate) can be made into a perfect one-way transducer using feed-forward

# All

An application of quantum communications is the transmission of qubits to

create shared symmetric encryption keys in a process called Quantum Key

Distribution (QKD). Contrary to public-private key encryption, symmetric

encryption is safe from (quantum) computing attacks, i.e. it provides forward

security and is thus attractive for secure communications. In this paper we

argue that for free-space quantum communications, especially with satellites,

if one assumes that man-in-the-middle attacks can be detected by classical

The real stabilizer fragment of quantum mechanics was shown to have a

complete axiomatization in terms of the angle-free fragment of the ZX-calculus.

This fragment of the ZXcalculus--although abstractly elegant--is stated in

terms of identities, such as spider fusion which generally do not have

interpretations as circuit transformations. We complete the category CNOT

generated by the controlled not gate and the computational ancillary bits,

presented by circuit relations, to the real stabilizer fragment of quantum

The variational quantum eigensolver is one of the most promising approaches

for performing chemistry simulations using noisy intermediate-scale quantum

(NISQ) processors. The efficiency of this algorithm depends crucially on the

ability to prepare multi-qubit trial states on the quantum processor that

either include, or at least closely approximate, the actual energy eigenstates

of the problem being simulated while avoiding states that have little overlap

Monte Carlo simulations are performed in classical phase space for a

one-dimensional quantum harmonic crystal. Symmetrization effects for spinless

bosons and fermions are quantified. The algorithm is tested for a range of

parameters against exact results that use 20,000 energy levels. It is shown

that the singlet mean field approximation is very accurate at high

temperatures, and that the pair mean field approximation gives a systematic

improvement in the intermediate and low temperature regime. The latter is

Optical clocks based on atoms and ions achieve exceptional precision and

accuracy, with applications to relativistic geodesy, tests of relativity, and

searches for dark matter. Achieving such performance requires balancing

competing desirable features, including a high particle number, isolation of

atoms from collisions, insensitivity to motional effects, and high duty-cycle

operation. Here we demonstrate a new platform based on arrays of ultracold

strontium atoms confined within optical tweezers that realizes a novel

We describe how an ensemble of four-level atoms in the diamond-type

configuration can be applied to create a fully controllable effective coupling

between two cavity modes. The diamond-type configuration allows one to use a

bimodal cavity that supports modes of different frequencies or different

circular polarisations, because each mode is coupled only to its own

transition. This system can be used for mapping a quantum state of one cavity

mode onto the other mode on demand. Additionally, it can serve as a fast

In the past decades, quantum plasmonics has become an active area due to its

potential applications in on-chip plasmonic devices for quantum information

processing. However, the fundamental physical process, i.e., how a quantum

state of light evolves in the photon-plasmon conversion process, has not been

clearly understood. Here, we report a complete characterization of the

plasmon-assisted extraordinary optical transmission process through quantum

process tomography. By inputting various coherent states to interact with the

A device-independent dimension test for a Bell experiment aims to estimate

the underlying Hilbert space dimension that is required to produce given

measurement statistical data without any other assumptions concerning the

quantum apparatus. Previous work mostly deals with the two-party version of

this problem. In this paper, we propose a very general and robust approach to

test the dimension of any subsystem in a multiparty Bell experiment. Our

dimension test stems from the study of a new multiparty scenario which we call

Hybrid quantum systems have the potential of mitigating current challenges in

developing a scalable quantum computer. Of particular interest is the

hybridization between atomic and superconducting qubits. We demonstrate a novel

experimental setup for transferring and trapping ultracold atoms inside a

millikelvin cryogenic environment, where interactions between atomic and

superconducting qubits can be established, paving the way for hybrid quantum

systems. $^{87}\text{Rb}$ atoms are prepared in a conventional magneto-optical