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80
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Introduction
Radu is currently a Senior researcher (CS 1) in the Department of Theoretical Physics (DFT), Horia Hulubei National Institute for Physics and Nuclear Engineering. Radu does research in Quantum Physics and Theoretical Physics. One if his recent publications is 'Interferometric mass spectrometry'.
Current institution
Current position
- Senior Researcher
Additional affiliations
February 2014 - November 2016
January 2013 - present
Position
- Senior Researcher I
January 2007 - October 2009
Education
October 1995 - January 1999
October 1993 - January 1994
September 1986 - June 1991
Publications
Publications (80)
Quantum communications introduce a paradigm change in internet security by using quantum resources to establish secure keys between parties. Present-day quantum communication networks are mainly point to point and use trusted nodes and key management systems to relay the keys. Future quantum networks, including the quantum internet, will have compl...
Accelerator mass spectrometry (AMS) is a widely used technique with multiple applications, including geology, molecular biology, and archeology. In order to achieve a high dynamic range, AMS requires tandem accelerators and large magnets, which thus confines it to big laboratories. Here we propose interferometric mass spectrometry (Interf-MS), a no...
Quantum communications bring a paradigm change in internet security by using quantum resources to establish secure keys between parties. Present-day quantum communications networks are mainly point-to-point and use trusted nodes and key management systems to relay the keys. Future quantum networks, including the quantum internet, will have complex...
Entangled photons are crucial for the development of quantum technologies and especially important in quantum communications. Hence it is paramount to have a reliable, high-fidelity source of entangled photons. Here we describe the construction and characterization of a polarization-entangled photon source. We generate maximally-entangled Bell stat...
Quantum imaging, one of the pillars of quantum technologies, is well suited to study sensitive samples which require low-light conditions, like biological tissues. In this context, interaction-free measurements (IFM) allow us to infer the presence of an opaque object without the photon interacting with the sample. Current IFM schemes are designed f...
Accelerator mass spectrometry (AMS) is a widely-used technique with multiple applications, including geology, molecular biology and archeology. Although extremely precise, AMS requires tandem accelerators and bulky magnets which confines it to large laboratories. Here we propose interferometric mass spectrometry (IMS), a novel method of mass separa...
Quantum imaging, one of the pillars of quantum technologies, is well-suited to study sensitive samples which require low-light conditions, like biological tissues. In this context, interaction-free measurements (IFM) allow us infer the presence of an opaque object without the photon interacting with the sample. Current IFM schemes are designed for...
Quantum technologies, such as quantum communication, quantum sensing, quantum imaging and quantum computation, need a platform which is flexible, miniaturisable and works at room temperature. Integrated photonics is a promising and fast-developing platform. This requires to develop the right tools to design and fabricate arbitrary photonic quantum...
Photons carrying orbital angular momentum (OAM) are excellent qudits and are widely used in several applications, such as long distance quantum communication, d-dimensional teleportation and high-resolution imaging and metrology. All these protocols rely on quantum tomography to characterise the OAM state, which currently requires complex measureme...
Quantum technologies, such as quantum communication, sensing and imaging, need a platform which is flexible, miniaturizable and works at room temperature. Integrated photonics is a promising and fast-developing platform. This requires to develop the right tools to design and fabricate arbitrary photonic quantum devices. Here we present an algorithm...
Photons carrying orbital angular momentum (OAM) are excellent qudits and are widely used in several applications, such as long distance quantum communication, $d$-dimensional teleportation and high-resolution imaging and metrology. All these protocols rely on quantum tomography to characterise the OAM state, which currently requires complex measure...
One of the main challenges in quantum technologies is the ability to control individual quantum systems. This task becomes increasingly difficult as the dimension of the system grows. Here we propose a general setup for cyclic permutations Xd in d dimensions, a major primitive for constructing arbitrary qudit gates. Using orbital angular momentum s...
One of the main challenges in quantum technologies is the ability to control individual quantum systems. This task becomes increasingly difficult as the dimension of the system grows. Here we propose an efficient setup for cyclic permutations $X_d$ in $d$ dimensions, a major primitive for constructing arbitrary qudit gates. Using orbital angular mo...
Interferometry is a widely-used technique for precision measurements in both classical and quantum contexts. One way to increase the precision of phase measurements, for example in a Mach-Zehnder interferometer (MZI), is to use high-intensity lasers. In this paper we study the phase sensitivity of a MZI in two detection setups (difference intensity...
Interferometry is a widely used technique for precision measurements in both classical and quantum contexts. One way to increase the precision of phase measurements, for example, in a Mach-Zehnder interferometer (MZI), is to use high-intensity lasers. In this paper we study the phase sensitivity of a MZI in two detection setups (difference intensit...
This corrects the article DOI: 10.1038/ncomms5997.
We propose an integrated polarization beam splitter based on a two-dimensional photonic crystal of polymer cylinders in air, with a TE bandgap centered on a wavelength of λ=780nm. The novel design is tailored for two-photon absorption 3D laser direct writing in a polymeric photoresist. Using this fabrication method, we can obtain spatial features a...
Schrödinger's cat is one of the most striking paradoxes of quantum mechanics that reveals the counterintuitive aspects of the microscopic world. Here, I discuss the paradox in the framework of quantum information. Using a quantum networks formalism, I analyse the information flow between the atom and the cat. This reveals that the atom and the cat...
Measuring the state of a quantum system is a fundamental process in quantum mechanics and plays an essential role in quantum information and quantum technologies. One method to measure a quantum observable is to sort the system in different spatial modes according to the measured value, followed by single-particle detectors on each mode. Examples o...
Measuring the state of a quantum system is a fundamental process in quantum
mechanics and plays an essential role in quantum information and quantum
technologies. One method to measure a quantum observable is to sort the system
in different spatial modes according to the measured value, followed by
single-particle detectors on each mode. Examples o...
The Weltanschauung emerging from quantum theory clashes profoundly with our
classical concepts. Quantum characteristics like superposition, entanglement,
wave-particle duality, nonlocality, contextuality are difficult to reconcile
with our everyday intuition. In this article I survey some aspects of quantum
foundations and discuss intriguing connec...
Quantum information is a recently emerged, paradigm-changing field which lays the foundations for quantum technologies. In this article we overview this fascinating subject, introduce the main mathematical concepts (entanglement, teleportation etc) and discuss forthcoming technologies like quantum computation, quantum cryptography, quantum imaging...
Wave-particle duality, superposition and entanglement are among the most counterintuitive features of quantum theory. Their clash with our classical expectations motivated hidden-variable (HV) theories. With the emergence of quantum technologies, we can test experimentally the predictions of quantum theory versus HV theories and put strong restrict...
Hidden-variable models aim to reproduce the results of quantum theory and
satisfy our classical intuition. Their refutation is based on deriving
predictions that are different from those of quantum mechanics. Here instead we
study the mutual consistency of apparently reasonable classical assumptions. We
introduce a version of the delayed-choice exp...
We describe a new class of experiments designed to probe the foundations of
quantum mechanics. Using quantum controlling devices, we show how to attain a
freedom in temporal ordering of the control and detection of various phenomena.
We consider wave-particle duality in the context of quantum-controlled and the
entanglement-assisted delayed-choice...
Wave-particle duality, superposition and entanglement are among the most
counterintuitive aspects of quantum theory. Their clash with classical
intuition motivated construction of hidden variable (HV) theories designed to
remove or explain these "strange" quantum features, and contributed to the
development of quantum technologies. Quantum controll...
A fundamental problem in quantum information is to describe efficiently multipartite quantum states. An efficient representation in terms of graphs exists for several families of quantum states (graph, cluster, and stabilizer states), motivating us to extend this construction to other classes. We introduce an axiomatic framework for mapping graphs...
Gedanken experiments are important conceptual tools in the quest to
reconcile our classical intuition with quantum mechanics and nowadays
are routinely performed in the laboratory. An important open question is
the quantum behaviour of the controlling devices in such experiments. We
propose a framework to analyse quantum-controlled experiments and...
Gedanken experiments help to reconcile our classical intuition with quantum mechanics and nowadays are routinely performed in the laboratory. An important open question is the quantum behavior of the controlling devices in such experiments. We propose a framework to analyze quantum-controlled experiments and illustrate it by discussing a quantum ve...
A fundamental problem in quantum information is to describe efficiently multipartite quantum states. An efficient representation in terms of graphs exists for several families of quantum states (graph, cluster, stabilizer states), motivating us to extend this construction to other classes. We introduce an axiomatic framework for mapping graphs to q...
Gedanken experiments are important conceptual tools in the quest to reconcile our classical intuition with quantum mechanics and nowadays are routinely performed in the laboratory. An important open question is the quantum behaviour of the controlling devices in such experiments. We propose a framework to analyse quantum-controlled experiments and...
In a recent article (arXiv:1006.1728) K.Michielsen et al. claim that a simple corpuscular model can explain many quantum optics experiments. We discuss these claims and show that their proposal fails at several levels. Finally, we propose an experiment to falsify the model.
Large scale quantum information processing (QIP) and distributed quantum computation require the ability to perform entangling operations on a large number of qubits. We describe a new photonic module which prepares, deterministically, photonic cluster states using an atom in a cavity as an ancilla. Based on this module we design a network for cons...
We present quantum networks for a n-qubit controlled gate C^{n-1}(U) which use a higher dimensional (qudit) ancilla as a catalyser. In its simplest form the network has only n two-particle gates (qubit-qudit) -- this is the minimum number of two-body interactions needed to couple all n+1 subsystems (n qubits plus one ancilla). This class of control...
Large scale quantum information processing (QIP) and distributed quantum computation require the ability to perform entangling operations on a large number of qubits. We describe a new photonic module which prepares, deterministically, photonic cluster states using an atom in a cavity as an ancilla. Based on this module we design a network for cons...
We present quantum networks for a n-qubit controlled gate C^{n-1}(U) which use a higher dimensional (qudit) ancilla as a catalyser. In its simplest form the network has only n two-particle gates (qubit-qudit) -- this is the minimum number of two-body interactions needed to couple all n+1 subsystems (n qubits plus one ancilla). This class of control...
Measurements play an important role in quantum computing (QC), by either providing the nonlinearity required for two-qubit gates (linear optics QC), or by implementing a quantum algorithm using single-qubit measurements on a highly entangled initial state (cluster state QC). Parity measurements can be used as building blocks for preparing arbitrary...
Measurements play an important role in quantum computing (QC), by either providing the nonlinearity required for two-qubit gates (linear optics QC), or by implementing a quantum algorithm using single-qubit measurements on a highly entangled initial state (cluster state QC). Parity measurements can be used as building blocks for preparing arbitrary...
Photonic entanglement has a wide range of applications in quantum computation and communication. Here we introduce a new device: the "photonic module", which allows for the rapid, deterministic preparation of a large class of entangled photon states. The module is an application independent, "plug and play" device, with sufficient flexibility to pr...
Matrix product states, a key ingredient of numerical algorithms widely employed in the simulation of quantum spin chains, provide an intriguing tool for quantum phase transition engineering. At critical values of the control parameters on which their constituent matrices depend, singularities in the expectation values of certain observables can app...
Photonic entanglement has a wide range of applications in quantum computation and communication. Here we introduce a new device: the "photonic module", which allows for the rapid, deterministic preparation of a large class of entangled photon states. The module is an application independent, "plug and play" device, with sufficient flexibility to pr...
The parity gate emerged recently as a promising resource for performing universal quantum computation with fermions using only linear interactions. Here we analyse the parity gate (P-gate) from a theoretical point of view in the context of quantum networks. We present several schemes for entanglement generation with P-gates and show that native net...
Matrix product states, a key ingredient of numerical algorithms widely employed in the simulation of quantum spin chains, provide an intriguing tool for quantum phase transition engineering. At critical values of the control parameters on which their constituent matrices depend, singularities in the expectation values of certain observables can app...
The parity gate emerged recently as a promising resource for performing universal quantum computation with fermions using only linear interactions. Here we analyse the parity gate (P-gate) from a theoretical point of view in the context of quantum networks. We present several schemes for entanglement generation with P-gates and show that native net...
We explore spintronics from a quantum information (QI) perspective. We show that QI specific methods can be an effective tool in designing new devices. Using the formalism of quantum gates acting on spin and mode degrees of freedom, we provide a solution to a reverse engineering problem, namely how to design a device performing a given transformati...
Given a finite group G with a bilocal representation, we investigate the bipartite entanglement in the state constructed from the group algebra of G acting on a separable reference state. We find an upper bound for the von Neumann entropy for a bipartition (A,B) of a quantum system and conditions to saturate it. We show that these states can be int...
Single spin measurement represents a major challenge for spin-based quantum computation. In this article we propose a new method for measuring the spin of a single electron confined in a quantum dot (QD). Our strategy is based on entangling (using unitary gates) the spin and orbital degrees of freedom. An {\em orbital qubit}, defined by a second, e...
Given a finite group G with a bilocal representation, we investigate the bipartite entanglement in the state constructed from the group algebra of G acting on a separable reference state. We find an upper bound for the von Neumann entropy for a bipartition (A,B) of a quantum system and conditions to saturate it. We show that these states can be int...
We study the entanglement properties of the ground state in Kitaev's
model. This is a two-dimensional spin system with a torus topology and
non-trivial four-body interactions between its spins. For a generic
partition (A,B) of the lattice we calculate analytically the von Neumann
entropy of the reduced density matrix ρA in the ground
state. We prov...
We investigate bipartite entanglement in spin-1∕2 systems on a generic lattice. For states that are an equal superposition of elements of a group G of spin flips acting on the fully polarized state ∣0⟩⊗n, we find that the von Neumann entropy depends only on the boundary between the two subsystems A and B. These states are stabilized by the group G....
We investigate bipartite entanglement in spin-1/2 systems on a generic lattice. For states that are an equal superposition of elements of a group $G$ of spin flips acting on the fully polarized state $\ket{0}^{\otimes n}$, we find that the von Neumann entropy depends only on the boundary between the two subsystems $A$ and $B$. These states are stab...
We describe and discuss a solid state proposal for quantum computation with mobile spin qubits in one-dimensional systems, based on recent advances in spintronics. Static electric fields are used to implement a universal set of quantum gates, via the spin-orbit and exchange couplings. Initialization and measurement can be performed either by spin i...
We discuss several aspects of a recently proposed mesoscopic spin-polarizing beam splitter (Ionicioiu R and D'Amico I 2003 Phys. Rev. B 67 041307(R)). The device can be used for both spin preparation and measurement and can be viewed as the mesoscopic analogue of a Stern–Gerlach apparatus. We also discuss how it can be used as an orientable Stern–G...
We investigate two models for performing topological quantum gates with the Aharonov-Bohm (AB) and Aharonov-Casher (AC) effects. Topological one- and two-qubit Abelian phases can be enacted with the AB effect using charge qubits, whereas the AC effect can be used to perform all single-qubit gates (Abelian and non-Abelian) for spin qubits. Possible...
We investigate two models for performing topological quantum gates with the Aharonov-Bohm (AB) and Aharonov-Casher (AC) effects. Topological one- and two-qubit Abelian phases can be enacted with the AB effect using charge qubits, whereas the AC effect can be used to perform all single-qubit gates (Abelian and non-Abelian) for spin qubits. Possible...
Spin preparation and spin detection are fundamental problems in spintronics and in several solid state proposals for quantum information processing. Here we propose the mesoscopic equivalent of an optical polarizing beam splitter (PBS). This interferometric device uses non-dispersive phases (Aharonov-Bohm and Rashba) in order to separate spin up an...
We consider a class of models of self-interacting bosons hopping on a lattice. We show that properly tailored space-temporal coherent control of the single-body coupling parameters allows for universal quantum computation in a given sector of the global Fock space. This general strategy for encoded universality in bosonic systems has in principle s...
Spin preparation and spin detection are fundamental problems in spintronics and in several solid state proposals for quantum information processing. Here we propose the mesoscopic equivalent of an optical polarizing beam splitter (PBS). This interferometric device uses non-dispersive phases (Aharonov-Bohm and Rashba) in order to separate spin up an...
We consider a class of models of self-interacting bosons hopping on a lattice. We show that properly tailored space-temporal coherent control of the single-body coupling parameters allows for universal quantum computation in a given sector of the global Fock space. This general strategy for encoded universality in bosonic systems has in principle s...
A review of semiconductor-based schemes for the implementation of quantum information processing devices is presented. After recalling the fundamentals of quantum information/computation theory, we shall discuss two potential implementation schemes based on charge degrees of freedom in semiconductor nanostructures. More specifically, we shall prese...
A three-beam configuration is used to investigate the spectrally resolved wave-mixing signal of a ZnSe single quantum well. The spectrum recorded in direction 2k 2-k 1 shows coherent oscillations induced by a delayed third pulse with direction k 3. Intensity and polarization-dependent measurements indicate that the signal is generated by a combinat...
A system able to produce entangled two-electron states is proposed and studied by means of numerical simulations. The basic device consists of a couple of semiconductor quantum wires in which single electrons are injected and propagated coherently. Coulomb coupling between two electrons in two different wires arises in a region where the wires get...
We shall review two implementation proposals for quantum information processing based on charge degrees-of-freedom in semiconductor nanostructures. An all-optical implementation scheme using semiconductor macroatoms/molecules will be discussed. The computational degrees-of-freedom in this proposal are interband optical transitions driven by ultrafa...
We shall review two implementation proposals for quantum information processing based on charge degrees of freedom in semiconductor nanostructures. An all-optical implementation scheme using semiconductor macroatoms/molecules will be discussed. The computational degrees of freedom in this proposal are interband optical transitions driven by ultrafa...
A review of semiconductor-based schemes for the implementation of quantum information processing devices is presented. After recalling the fundamentals of quantum information/computation theory, we shall discuss two potential implementation schemes based on charge degrees of freedom in semiconductor nanostructures. More specifically, we shall prese...
We propose an experiment to test Bell's inequality violation in condensed-matter physics. We show how to generate, manipulate and detect entangled states using ballistic electrons in Coulomb-coupled semiconductor quantum wires. Due to its simplicity (only five gates are required to prepare entangled states and to test Bell's inequality), the propos...
We describe a solid state implementation of a quantum computer using ballistic single electrons as flying qubits in 1D nanowires. We show how to implement all the steps required for universal quantum computation: preparation of the initial state, measurement of the final state and a universal set of quantum gates. An important advantage of this mod...
We describe a solid state implementation of a quantum computer using ballistic single electrons as flying qubits in 1D nanowires. We show how to implement all the steps required for universal quantum computation: preparation of the initial state, measurement of the final state and a universal set of quantum gates. An important advantage of this mod...
We propose an experiment to test Bell's inequality violation in condensed-matter physics. We show how to generate, manipulate and detect entangled states using ballistic electrons in Coulomb-coupled semiconductor quantum wires. Due to its simplicity (only five gates are required to prepare entangled states and to test Bell's inequality), the propos...
We give a brief introduction to quantum computation and we discuss
a possible solid state implementation. We show how to prepare and
measure qubit states and how to implement single and 2-qubit gates with
ballistic electrons
We propose a new solid state implementation of a quantum computer (quputer) using ballistic single electrons as flying qubits in 1D nanowires. We use a single electron pump (SEP) to prepare the initial state and a single electron transistor (SET) to measure the final state. Single qubit gates are implemented using quantum dots as phase shifters and...
We calculate partition functions for lens spaces L-p,L-q up to p = 8 and for genus-1 and -2 handlebodies H-1, H-2 in the Turaev-Viro framework. These can be interpreted as transition amplitudes in three-dimensional quantum gravity. in the case of lens spaces L-p,L-q these are vacuum-to-vacuum amplitudes circle divide --> circle divide, whereas for...
We investigate the Turaev-Viro invariant (partition function) for 3-manifolds with a boundary. In the framework of a TQFT, the partition function of such a manifold can be interpreted as a transition amplitude for topology change in 3D gravity. We show that for boundaries factorizes into a term which contains the boundary dependence and another whi...
In this letter we show that in a Kaluza-Klein framework we can have arbitrary topology change between the macroscopic (i.e. noncompactified) spacelike 3-hypersurfaces. This is achieved by using the compactified dimensions as a catalyser for topology change. In the case of odddimensional spacetimes (such as the 11-dimensional M-theory) this is alway...
We calculate partition functions for lens spaces L_{p,q} up to p=8 and for genus 1 and 2 handlebodies H_1, H_2 in the Turaev-Viro framework. These can be interpreted as transition amplitudes in 3D quantum gravity. In the case of lens spaces L_{p,q} these are vacuum-to-vacuum amplitudes $\O -> \O$, whereas for the 1- and 2-handlebodies H_1, H_2 they...
We investigate topology change in 3D. Using Morse theory and handle decomposition we find the set of elementary cobordisms for 3-manifolds. These are: (i) \O <-> S^2; (ii) \Sigma_g <-> \Sigma_{g+1}; (iii) \Sigma_{g_1} \sqcup \Sigma_{g_2} <-> \Sigma_{g_1+g_2} and they have appealing physical interpretations, e.g. Big Bang/Big Crunch, wormhole creati...
We study the form of the Turaev-Viro partition function Z(M) for different 3-manifolds with boundary. We show that for $S^2$ boundaries Z(M) factorizes into a term which contains the boundary dependence and another which depends only on the topology of the underlying manifold. From this follows easily the formula for the connected sum of two manifo...
We investigate bipartite entanglement in a class of multiparty quantum states, the ¡ -states, constructed from a group ¡ , and we derive an expression for the von Neumann entropy. We show that for a special subset of such states, the ¡ -homogeneous states, the entropy satisfies the area law. If ¡ is a group of spin-flips, the ¡ -homogeneous states...
