Quantum state tomography--deducing quantum states from measured data--is the gold standard for verification and benchmarking of quantum devices. It has been realized in systems with few components, but for larger systems it becomes unfeasible because the number of measurements and the amount of computation required to process them grows exponentially in the system size. Here, we present two tom...

We introduce a novel method for reconstructing quantum superposition states excited in molecules or atoms by short laser pulses. The technique is based on mixing the unknown object state with a known reference state generated in the same system by an additional delayed laser pulse, and detecting the total time-and frequency-integrated uorescence as a function of the delay. We demonstrate the fe...

We consider the problem of quantum state certification, where one is given n copies of an unknown d-dimensional quantum mixed state ρ, and one wants to test whether ρ is equal to some known mixed state σ or else is -far from σ. The goal is to use notably fewer copies than the Ω(d) needed for full tomography on ρ (i.e., density estimation). We give two robust state certification algorithms: one ...

Near-term quantum computers are noisy, and therefore must run algorithms with a low circuit depth qubit count. Here we investigate how noise affects neural network (QNN) for state discrimination, applicable on near-term devices as it fulfils the above criteria. We find that when simulating gradient calculation noisy device, large number of parameters is disadvantageous. By introducing new small...

We investigate the use of external time-dependent magnetic field for the control of the quantum states in a two-electron quantum ring. The hyperfine interaction of the confined electrons with surrounding nuclei couples the singlet state with the three triplet states. When the external magnetic field is changed, the singlet ground state becomes degenerate with the triplet states allowing singlet...

1Department of Physics, King’s College London, Strand, LondonWC2R 1LS, UK 2Mathematical Sciences, Brunel University, Uxbridge UB8 3PH, UK 3Physics Department, University of Chicago, Chicago, IL 60637, USA 4Helmholtz-Center Dresden-Rossendorf, PO Box 51 01 19, 01314 Dresden, Germany 5Department of Physics, Renmin University of China, Beijing 100872, People’s Republic of China 6Tomsk State Univer...

It is a fundamental consequence of the superposition principle for quantum states that there must exist non-orthogonal states, that is states that, although different, have a non-zero overlap. This finite overlap means that there is no way of determining with certainty in which of two such states a given physical system has been prepared. We review the various strategies that have been devised ...

It is experimentally demonstrated that an arbitrary quantum state of a single spin 1/2: ↓ + ↑ b a can be converted into a superposition of the two ferromagnetic states of a spin cluster: ↓↓ ↓↓ + ↑↑ ↑↑ b a . The physical system is a cluster of seven dipolar-coupled nuclear spins of single-labeled C-benzene molecules in a liquidcrystalline matrix. In this complex system, the pseudopure ground sta...

Quantum state tomography is the task of inferring the state of a quantum system by appropriate measurements. Since the frequency distributions of the outcomes of any finite number of measurements will generally deviate from their asymptotic limits, the estimates computed by standard methods do not in general coincide with the true state and, therefore, have no operational significance unless th...