# Dr Eran Ginossar

## Lecturer

Email: e.ginossar@surrey.ac.uk

Phone: Work: 01483 68 2714

Room no: 20 ATI 02

### Office hours

Please e-mail me to schedule a meeting or regarding applications for PhD (also see projects page )

## Further information

## Biography

Eran Ginossar grew up in Israel, where he obtained his BSc in Physics from Tel-Aviv University. During his graduate

studies at the Weizmann Institute of Science in Rehovot he worked on extending the theory of optical spin

orientation of direct gap semiconductors to include the fluctuations of the light and of the spins. After receiving

his PhD in 2008 he moved to Yale University to study the physics of superconducting circuits, a field that is

rapidly progressing in creating viable devices for quantum information processing. Additional topics of interest

include interaction effects in mesoscopic systems, quantum optics and quantum simulations. Eran has joined the

Department of Physics and the Advanced Technology Institute at the University of Surrey in 2011. He is a member of

the APS and an EPSRC fellow.

## Research Interests

Circuit Quantum Electrodynamics: Measurement theory and control of Qubits and Resonators. These projects are geared towards developing the building blocks and protocols for quantum information processing with solid state devices. My research in this field is strongly motivated by experiments which routinely raise research questions in quantum optics and coherent control. The methodology involves taking a non-equilibrium open system approach to modeling and employing large scale computer simulations.

Semiconductor quantum optics: The theory of optical spin orientation of direct gap semiconductors can include the fluctuations of the light and of the spins. Our analysis treats the effects of optical photonic correlations, present in down converted light, on the collective fluctuations of the spins excited by the light. This shows a possibility to control the temporal fluctuations of the collective electronic spin in actual semiconductor devices, demonstrating that quantum optical effects can appear in the optical absorption of squeezed light by a semiconductor.

Mesoscopic physics: Electronic interferometers in the quantum Hall state, persistent currents in normal metal rings, random lasers.

## Publications

### Highlights

- 'Microwave transitions as a signature of coherent parity mixing effects in the Majorana-transmon qubit.'.
Nat Commun, England: 5doi: 10.1038/ncomms5772
#### Abstract

Solid-state Majorana fermions are generating intensive interest because of their unique properties and possible applications in fault tolerant quantum memory devices. Here we propose a method to detect signatures of Majorana fermions in hybrid devices by employing the sensitive apparatus of the superconducting charge-qubit architecture and its efficient coupling to microwave photons. In the charge and transmon regimes of this device, we find robust signatures of the underlying Majorana fermions that are, remarkably, not washed out by the smallness of the Majorana contribution to the Josephson current. It is predicted that at special gate bias points the photon-qubit coupling can be switched off via quantum interference, and in other points it is exponentially dependent on the control parameter EJ/EC. We propose that this device could be used to manipulate the quantum state of the Majorana fermion and realize a tunable high coherence four-level system in the superconducting-circuit architecture.

.
(2014) - 'Tunability of microwave transitions as a signature of coherent parity
mixing effects in the Majorana-Transmon qubit'.
Nat. Commun. 5, 4772 (2014), doi: 10.1038/ncomms5772
**Full text**is available at: http://epubs.surrey.ac.uk/790667/#### Abstract

Coupling Majorana fermion excitations to coherent external fields is an important stage towards their manipulation and detection. We analyse the charge and transmon regimes of a topological nano-wire embedded within a Cooper-Pair-Box, where the superconducting phase difference is coupled to the zero energy parity states that arise from Majorana quasi-particles. We show that at special gate bias points, the photon-qubit coupling can be switched off via quantum interference, and in other points it is exponentially dependent on the control parameter $E_J/E_C$. As well as a probe for topological-superconductor excitations, we propose that this type of device could be used to realise a tunable high coherence four-level system in the superconducting circuits architecture.

.
(2013) - 'Reduction of the radiative decay of atomic coherence in squeezed vacuum.'.
Nature, England: 499 (7456), pp. 62-65.doi: 10.1038/nature12264
#### Abstract

Quantum fluctuations of the electromagnetic vacuum are responsible for physical effects such as the Casimir force and the radiative decay of atoms, and set fundamental limits on the sensitivity of measurements. Entanglement between photons can produce correlations that result in a reduction of these fluctuations below the ordinary vacuum level, allowing measurements that surpass the standard quantum limit in sensitivity. The effects of such 'squeezed states' of light on matter were first considered in a prediction of the radiative decay rates of atoms in squeezed vacuum. Despite efforts to demonstrate such effects in experiments with natural atoms, a direct quantitative observation of this prediction has remained elusive. Here we report a twofold reduction of the transverse radiative decay rate of a superconducting artificial atom coupled to continuum squeezed vacuum. The artificial atom is effectively a two-level system formed by the strong interaction between a superconducting circuit and a microwave-frequency cavity. A Josephson parametric amplifier is used to generate quadrature-squeezed electromagnetic vacuum. The observed twofold reduction in the decay rate of the atom allows the transverse coherence time, T2, to exceed the ordinary vacuum decay limit, 2T1. We demonstrate that the measured radiative decay dynamics can be used to reconstruct the Wigner distribution of the itinerant squeezed state. Our results confirm a canonical prediction of quantum optics and should enable new studies of the quantum light-matter interaction.

.
(2013) - 'Response of the strongly driven Jaynes-Cummings oscillator.'.
Phys Rev Lett, United States: 105 (10) Article number 100505
**Full text**is available at: http://epubs.surrey.ac.uk/38233/#### Abstract

We analyze the Jaynes-Cummings model of quantum optics, in the strong-dispersive regime. In the bad-cavity limit and on time scales short compared to the atomic coherence time, the dynamics are those of a nonlinear oscillator. A steady-state nonperturbative semiclassical analysis exhibits a finite region of bistability delimited by a pair of critical points, unlike the usual dispersive bistability from a Kerr nonlinearity. This analysis explains our quantum trajectory simulations that show qualitative agreement with recent experiments from the field of circuit quantum electrodynamics.

.
(2010) - 'Persistent currents in normal metal rings.'.
Science, United States: 326 (5950), pp. 272-275.
#### Abstract

Quantum mechanics predicts that the equilibrium state of a resistive metal ring will contain a dissipationless current. This persistent current has been the focus of considerable theoretical and experimental work, but its basic properties remain a topic of controversy. The main experimental challenges in studying persistent currents have been the small signals they produce and their exceptional sensitivity to their environment. We have developed a technique for detecting persistent currents that allows us to measure the persistent current in metal rings over a wide range of temperatures, ring sizes, and magnetic fields. Measurements of both a single ring and arrays of rings agree well with calculations based on a model of non-interacting electrons.

.
(2009) - 'Behavior of electronic interferometers in the nonlinear regime.'.
Phys Rev Lett, United States: 100 (19) Article number 196806
**Full text**is available at: http://epubs.surrey.ac.uk/37672/#### Abstract

We investigate theoretically the behavior of the current oscillations in an electronic Mach-Zehnder interferometer (MZI) as a function of its source bias. Recently, the MZI visibility data showed an unexplained lobe pattern with a peculiar phase rigidity. Moreover, the effect did not depend on the MZI path length difference. We argue that these effects may be a new many-body manifestation of particle-wave duality in quantum mechanics. When biasing the interferometer sources so much that multiple electrons are on each arm at any instant in time, quantum shot noise (a particle phenomena) must affect the interference pattern of the electrons that create it. A solution to the interaction Hamiltonian presented here shows that the interference visibility has a lobe pattern with applied bias that has a period proportional to the average path length and independent of the path length difference, together with a phase rigidity.

.
(2008)

### Journal articles

- 'Fermion parity measurement and control in Majorana circuit quantum
electrodynamics'.
#### Abstract

Combining superconducting qubits with mesoscopic devices that carry topological states of matter may lead to compact and improved qubit devices with properties useful for fault-tolerant quantum computation. Recently, a charge qubit device based on a topological superconductor circuit has been introduced where signatures of Majorana fermions could be detected spectroscopically in the transmon regime. This device stores quantum information in coherent superpositions of fermion parity states originating from the Majorana fermions, generating a highly isolated qubit whose coherence time could be greatly enhanced. We extended the conventional semi-classical method and obtained analytical derivations for strong transmon-photon coupling. The analytical challenge is rendered tractable via a formalism based on the WKB method that allows to extract the energy eigenstates of the qubit and its dipole matrix elements. Using this formalism, we study the effect of the Majorana fermions on the quantum electrodynamics of the device embedded within an optical cavity and develop protocols to initialise, control and measure the parity states. We show that, remarkably, the parity eigenvalue can be detected via dispersive shifts of the optical cavity in the strong coupling regime and its state can be coherently manipulated via a second order sideband transition.

.
(2014) - 'Microwave transitions as a signature of coherent parity mixing effects in the Majorana-transmon qubit.'.
Nat Commun, England: 5doi: 10.1038/ncomms5772
#### Abstract

Solid-state Majorana fermions are generating intensive interest because of their unique properties and possible applications in fault tolerant quantum memory devices. Here we propose a method to detect signatures of Majorana fermions in hybrid devices by employing the sensitive apparatus of the superconducting charge-qubit architecture and its efficient coupling to microwave photons. In the charge and transmon regimes of this device, we find robust signatures of the underlying Majorana fermions that are, remarkably, not washed out by the smallness of the Majorana contribution to the Josephson current. It is predicted that at special gate bias points the photon-qubit coupling can be switched off via quantum interference, and in other points it is exponentially dependent on the control parameter EJ/EC. We propose that this device could be used to manipulate the quantum state of the Majorana fermion and realize a tunable high coherence four-level system in the superconducting-circuit architecture.

.
(2014) - 'Tunability of microwave transitions as a signature of coherent parity
mixing effects in the Majorana-Transmon qubit'.
Nat. Commun. 5, 4772 (2014), doi: 10.1038/ncomms5772
**Full text**is available at: http://epubs.surrey.ac.uk/790667/#### Abstract

Coupling Majorana fermion excitations to coherent external fields is an important stage towards their manipulation and detection. We analyse the charge and transmon regimes of a topological nano-wire embedded within a Cooper-Pair-Box, where the superconducting phase difference is coupled to the zero energy parity states that arise from Majorana quasi-particles. We show that at special gate bias points, the photon-qubit coupling can be switched off via quantum interference, and in other points it is exponentially dependent on the control parameter $E_J/E_C$. As well as a probe for topological-superconductor excitations, we propose that this type of device could be used to realise a tunable high coherence four-level system in the superconducting circuits architecture.

.
(2013) - 'Reduction of the radiative decay of atomic coherence in squeezed vacuum.'.
Nature, England: 499 (7456), pp. 62-65.doi: 10.1038/nature12264
#### Abstract

Quantum fluctuations of the electromagnetic vacuum are responsible for physical effects such as the Casimir force and the radiative decay of atoms, and set fundamental limits on the sensitivity of measurements. Entanglement between photons can produce correlations that result in a reduction of these fluctuations below the ordinary vacuum level, allowing measurements that surpass the standard quantum limit in sensitivity. The effects of such 'squeezed states' of light on matter were first considered in a prediction of the radiative decay rates of atoms in squeezed vacuum. Despite efforts to demonstrate such effects in experiments with natural atoms, a direct quantitative observation of this prediction has remained elusive. Here we report a twofold reduction of the transverse radiative decay rate of a superconducting artificial atom coupled to continuum squeezed vacuum. The artificial atom is effectively a two-level system formed by the strong interaction between a superconducting circuit and a microwave-frequency cavity. A Josephson parametric amplifier is used to generate quadrature-squeezed electromagnetic vacuum. The observed twofold reduction in the decay rate of the atom allows the transverse coherence time, T2, to exceed the ordinary vacuum decay limit, 2T1. We demonstrate that the measured radiative decay dynamics can be used to reconstruct the Wigner distribution of the itinerant squeezed state. Our results confirm a canonical prediction of quantum optics and should enable new studies of the quantum light-matter interaction.

.
(2013) - 'Suppression of the radiative decay of atomic coherence in squeezed
vacuum'.
Quantum Physics,
**Full text**is available at: http://epubs.surrey.ac.uk/749750/#### Abstract

Quantum fluctuations of the electromagnetic vacuum are responsible for physical effects such as the Casimir force and the radiative decay of atoms, and set fundamental limits on the sensitivity of measurements. Entanglement between photons can produce correlations that result in a reduction of these fluctuations below the vacuum level allowing measurements that surpass the standard quantum limit in sensitivity. Here we demonstrate that the radiative decay rate of an atom that is coupled to quadrature squeezed electromagnetic vacuum can be reduced below its natural linewidth. We observe a two-fold reduction of the transverse radiative decay rate of a superconducting artificial atom coupled to continuum squeezed vacuum generated by a Josephson parametric amplifier, allowing the transverse coherence time T_2 to exceed the vacuum decay limit of 2T_1. We demonstrate that the measured radiative decay dynamics can be used to tomographically reconstruct the Wigner distribution of the the itinerant squeezed state. Our results are the first confirmation of a canonical prediction of quantum optics and open the door to new studies of the quantum light-matter interaction.

.
(2013) - 'Observation of quantum state collapse and revival due to the single-photon Kerr effect'.
NATURE, 495 (7440), pp. 205-209.doi: 10.1038/nature11902
**Full text**is available at: http://epubs.surrey.ac.uk/749139/
.
(2012) - 'Quantum state sensitivity of an autoresonant superconducting circuit'.
Physical Review B - Condensed Matter and Materials Physics, 86 (22)
**Full text**is available at: http://epubs.surrey.ac.uk/729045/#### Abstract

When a frequency chirped excitation is applied to a classical high-Q nonlinear oscillator, its motion becomes dynamically synchronized to the drive and large oscillation amplitude is observed, provided the drive strength exceeds the critical threshold for autoresonance. We demonstrate that when such an oscillator is strongly coupled to a quantized superconducting qubit, both the effective nonlinearity and the threshold become a nontrivial function of the qubit-oscillator detuning. Moreover, the autoresonant threshold is dependent on the quantum state of the qubit and may be used to realize a high-fidelity, latching readout whose speed is not limited by the oscillator Q. © 2012 American Physical Society.

.
(2012) - 'High-cooperativity coupling of electron-spin ensembles to superconducting cavities.'.
Phys Rev Lett, United States: 105 (14) Article number 140501
**Full text**is available at: http://epubs.surrey.ac.uk/37910/#### Abstract

Electron spins in solids are promising candidates for quantum memories for superconducting qubits because they can have long coherence times, large collective couplings, and many qubits could be encoded into spin waves of a single ensemble. We demonstrate the coupling of electron-spin ensembles to a superconducting transmission-line cavity at strengths greatly exceeding the cavity decay rates and comparable to the spin linewidths. We also perform broadband spectroscopy of ruby (Al₂O₃:Cr(3+)) at millikelvin temperatures and low powers, using an on-chip feedline. In addition, we observe hyperfine structure in diamond P1 centers.

.
(2010) - 'Quantum non-demolition detection of single microwave photons in a circuit'.
NATURE PHYSICS, 6 (9), pp. 663-667.doi: 10.1038/NPHYS1710
**Full text**is available at: http://epubs.surrey.ac.uk/732760/
.
(2010) - 'Response of the strongly driven Jaynes-Cummings oscillator.'.
Phys Rev Lett, United States: 105 (10) Article number 100505
**Full text**is available at: http://epubs.surrey.ac.uk/38233/#### Abstract

We analyze the Jaynes-Cummings model of quantum optics, in the strong-dispersive regime. In the bad-cavity limit and on time scales short compared to the atomic coherence time, the dynamics are those of a nonlinear oscillator. A steady-state nonperturbative semiclassical analysis exhibits a finite region of bistability delimited by a pair of critical points, unlike the usual dispersive bistability from a Kerr nonlinearity. This analysis explains our quantum trajectory simulations that show qualitative agreement with recent experiments from the field of circuit quantum electrodynamics.

.
(2010) - 'Protocol for high-fidelity readout in the photon-blockade regime of circuit QED'.
PHYSICAL REVIEW A, 82 (2) Article number ARTN 022335
**Full text**is available at: http://epubs.surrey.ac.uk/38232/
.
(2010) - 'Mesoscopic persistent currents in a strong magnetic field'.
PHYSICAL REVIEW B, 81 (15) Article number ARTN 155448
**Full text**is available at: http://epubs.surrey.ac.uk/37945/
.
(2010) - 'Persistent currents in normal metal rings.'.
Science, United States: 326 (5950), pp. 272-275.
#### Abstract

Quantum mechanics predicts that the equilibrium state of a resistive metal ring will contain a dissipationless current. This persistent current has been the focus of considerable theoretical and experimental work, but its basic properties remain a topic of controversy. The main experimental challenges in studying persistent currents have been the small signals they produce and their exceptional sensitivity to their environment. We have developed a technique for detecting persistent currents that allows us to measure the persistent current in metal rings over a wide range of temperatures, ring sizes, and magnetic fields. Measurements of both a single ring and arrays of rings agree well with calculations based on a model of non-interacting electrons.

.
(2009) - 'Proposal for generating and detecting multi-qubit GHZ states in circuit QED'.
NEW JOURNAL OF PHYSICS, 11 Article number ARTN 073040
**Full text**is available at: http://epubs.surrey.ac.uk/38235/
.
(2009) - 'Coherent optical control of correlation waves of spins in semiconductors'.
PHYSICAL REVIEW B, 78 (20) Article number ARTN 205204
**Full text**is available at: http://epubs.surrey.ac.uk/37878/
.
(2008) - 'Behavior of electronic interferometers in the nonlinear regime.'.
Phys Rev Lett, United States: 100 (19) Article number 196806
**Full text**is available at: http://epubs.surrey.ac.uk/37672/#### Abstract

We investigate theoretically the behavior of the current oscillations in an electronic Mach-Zehnder interferometer (MZI) as a function of its source bias. Recently, the MZI visibility data showed an unexplained lobe pattern with a peculiar phase rigidity. Moreover, the effect did not depend on the MZI path length difference. We argue that these effects may be a new many-body manifestation of particle-wave duality in quantum mechanics. When biasing the interferometer sources so much that multiple electrons are on each arm at any instant in time, quantum shot noise (a particle phenomena) must affect the interference pattern of the electrons that create it. A solution to the interaction Hamiltonian presented here shows that the interference visibility has a lobe pattern with applied bias that has a period proportional to the average path length and independent of the path length difference, together with a phase rigidity.

.
(2008) - 'Optical manipulation of collective spin correlations in semiconductors with a squeezed vacuum of polarized photons'.
PHYSICAL REVIEW B, 77 (3) Article number ARTN 035307
**Full text**is available at: http://epubs.surrey.ac.uk/37935/
.
(2008) - 'Atom in a coherently controlled squeezed vacuum'.
PHYSICAL REVIEW A, 76 (1) Article number ARTN 013821
**Full text**is available at: http://epubs.surrey.ac.uk/37618/
.
(2007) - 'Semiconductor Microstructure in a Squeezed Vacuum: Electron-Hole Plasma
Luminescence'.
Physical Review B (Condensed Matter and Materials Physics), 72 (7) Article number 075333
**Full text**is available at: http://epubs.surrey.ac.uk/13488/#### Abstract

We consider a semiconductor quantum-well placed in a wave guide microcavity and interacting with the broadband squeezed vacuum radiation, which fills one mode of the wave guide with a large average occupation. The wave guide modifies the optical density of states so that the quantum well interacts mostly with the squeezed vacuum. The vacuum is squeezed around the externally controlled central frequency $\om_0$, which is tuned above the electron-hole gap $E_g$, and induces fluctuations in the interband polarization of the quantum-well. The power spectrum of scattered light exhibits a peak around $\om_0$, which is moreover non-Lorentzian and is a result of both the squeezing and the particle-hole continuum. The squeezing spectrum is qualitatively different from the atomic case. We discuss the possibility to observe the above phenomena in the presence of additional non-radiative (e-e, phonon) dephasing.

.
(2005)

### Book chapters

- 'Nonlinear oscillators and high fidelity qubit state measurement in
circuit quantum electrodynamics'. in (ed.)
*Fluctuating Nonlinear Oscillators. From nanomechanics to quantum superconducting circuits*Oxford University Press Article number 8#### Abstract

In this book chapter we analyze the high excitation nonlinear response of the Jaynes-Cummings model in quantum optics when the qubit and cavity are strongly coupled. We focus on the parameter ranges appropriate for transmon qubits in the circuit quantum electrodynamics architecture, where the system behaves essentially as a nonlinear quantum oscillator and we analyze the quantum and semi-classical dynamics. One of the central motivations is that under strong excitation tones, the nonlinear response can lead to qubit quantum state discrimination and we present initial results for the cases when the qubit and cavity are on resonance or far off-resonance (dispersive).

.
(2012)

### Internet publications

- Universal Features of Interacting Chaotic Quantum Dots. Application to
Statistics of Coulomb Blockade Peak Spacings.
**Full text**is available at: http://epubs.surrey.ac.uk/729046/#### Abstract

We present a complete classification of the electron-electron interaction in chaotic quantum dots based on expansion in inverse powers of $1/M$, the number of the electron states in the Thouless window, $M \simeq k_F R$. This classification is quite universal and extends and enlarges the universal non interacting RMT statistical ensembles. We show that existing Coulomb blockade peak spacing data for $B=0$ and $B\ne 0$ is described quite accurately by the interacting GSE and by its extension to $B\ne 0$. The bimodal structure existing in the interacting GUE case is completely washed out by the combined effect of the spin orbit, pairing and higher order residual interactions.

.
(2001)

## Teaching

Level 1 Essential Mathematics

Advanced Quantum Physics