Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Log inSign up
Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Blog
Job Board
Q3AS

© 2026 Aqora Quantum S.A.S.

TermsPrivacyLegal Notice

arXiv:2111.14890 · Physical Review A

Demonstration of quantum-limited discrimination of multicopy pure versus mixed states

Arunkumar Jagannathan, Michael R. Grace, Olivia Brasher, Jeffrey H. Shapiro, Saikat Guha, Jonathan L. Habif

Published Mar 25, 2022• 8 citations
arXivHTMLPDF

Abstract

We demonstrate an optical receiver that achieves the quantum Chernoff bound for discriminating coherent states from thermal states in the multicopy scenario. In contrast, we find that repeated use of the receiver approaching the Helstrom bound for single-copy measurement is suboptimal in this multicopy case. Furthermore, for a large class of multicopy discrimination tasks between a pure and a mixed state, we prove that any Helstrom-bound achieving single-copy receiver is suboptimal by a factor of at least 2 in error-probability exponent compared to the multicopy quantum Chernoff bound. This behavior has a classical analog in the performance gap between soft-decision and hard-decision receivers for detecting a multicopy signal embedded in white Gaussian noise.

DOI
10.1103/physreva.105.032446

Related papers

Realizable receivers for discriminating coherent and multicopy quantum states near the quantum limit

Ranjith Nair, Saikat Guha, Si-Hui Tan

We derive the quantum limit on the error probability exponent for discriminating any $M$ multimode coherent states of light and show that it is four times that of an ideal heterodyne receiver for the same signal set. We then propose a receiver that achieves the quantum limit using auxiliary coherent-state fields, beam splitters, and single-photon detectors. The performance of the receiver is compared to standard measurements for various imaging and communication tasks. A related receiver for discriminating arbitrary multicopy pure quantum states is shown to achieve the $M$-ary quantum Chernoff exponent and does so using only local operations and classical communication.

arXiv:1212.2048•Physical Review A•Mar 12, 2014•40 citations

Attainability of quantum state discrimination bounds with collective measurements on finite copies

Lorcán O. Conlon, Jin Ming Koh, Biveen Shajilal +3 more

One of the fundamental tenets of quantum mechanics is that nonorthogonal states cannot be distinguished perfectly. When distinguishing multiple copies of a mixed quantum state, a collective measurement, which generates entanglement between the different copies of the unknown state, can achieve a lower error probability than nonentangling measurements. The error probability that can be attained using a collective measurement on a finite number of copies of the unknown state is given by the Helstrom bound. In the limit where we can perform a collective measurement on asymptotically many copies of the quantum state, the quantum Chernoff bound gives the attainable error probability. It is natural to ask, then, what strategies can be employed to reach these two bounds---is entanglement across all available modes always necessary or can other, experimentally more simple measurements saturate these bounds? In this work we address this question. We find analytic expressions for the Helstrom bound for arbitrarily many copies of the unknown state in simple qubit examples. Using these analytic expressions, we investigate whether the quantum Chernoff bound can be saturated by repeatedly implementing the $M$-copy Helstrom measurement. We also investigate the necessary conditions to saturate the $M$-copy Helstrom bound. It is known that a collective measurement on all $M$ copies of the unknown state is always sufficient to saturate the $M$-copy Helstrom bound. However, general conditions for when such a measurement is necessary to saturate the Helstrom bound remain unknown. We investigate specific measurement strategies which involve entangling operations on fewer than all $M$ copies of the unknown state. For many regimes we find that a collective measurement on all $M$ copies of the unknown state is necessary to saturate the $M$-copy Helstrom bound.

arXiv:2408.06678•Physical Review A•Feb 21, 2025•2 citations

A realizable receiver for discriminating arbitrary coherent states near the quantum limit

Ranjith Nair, Saikat Guha, Si-Hui Tan

Discriminating coherent states of light is an important instance of quantum state discrimination that is central to all applications of laser light. We obtain the ultimate quantum limit on the error probability exponent for discriminating among any M multimode coherent-state signals via the recently developed theory of the quantum Chernoff exponent in M-ary multi-copy state discrimination. A receiver called the Sequential Waveform Nulling (SWN) receiver is proposed for discriminating an arbitrary coherent-state ensemble using only auxiliary coherent-state fields, beam splitters, and non-number-resolving single photon detectors. An explicit error probability analysis of the SWN receiver is used to show that it achieves the quantum limit on the error probability exponent, which is shown to be a factor of four greater than the error probability exponent of an ideal heterodyne-detection receiver on the same ensemble. Apart from being of fundamental interest, these results are relevant to communication, sensing, imaging, and quantum information processing systems that use laser light.

IEEE International Symposium on Information Theory (ISIT)•Jul 1, 2013•0 citations

Quantum-limited discrimination of laser light and thermal light

Jonathan L. Habif, Arunkumar Jagannathan, Samuel Gartenstein +2 more

Understanding the fundamental sensitivity limit of an optical sensor requires a full quantum mechanical description of the sensing task. In this work, we calculate the fundamental (quantum) limit for discriminating between pure laser light and thermal noise in a photon-starved regime. The Helstrom bound for discrimination error probability for single mode measurement is computed along with error probability bounds for direct detection, coherent homodyne detection and the Kennedy receiver. A generalized Kennedy (GK) receiver is shown to closely approach the Helstrom limit. We present an experimental demonstration of this sensing task and demonstrate a 15.4 dB improvement in discrimination sensitivity over direct detection using a GK receiver and an improvement of 19.4% in error probability over coherent detection.

arXiv:1912.06718•Optics Express•Feb 15, 2021•15 citations

Attainment of the multiple quantum Chernoff bound for certain ensembles of mixed states

Michael Nussbaum

We consider the problem of detecting the true quantum state among r possible ones, based on measurements performed on n of copies of a finite dimensional quantum system. It is known that the exponent for the rate of decrease of the averaged error probability cannot exceed the multiple quantum Chernoff bound (MQCB) defined as the worst case (smallest) quantum Chernoff distance between any possible pair of the r states. This error exponent is attainable for r pure states, but for the general case of mixed states only attainability up to a factor 1/3 is known. Here we show that the MQCB is attainable for mixed states if there is a pair which is closer in quantum Chernoff distance than 1/6 times the distance between all other pairs.

arXiv:1308.6563•Aug 29, 2013•3 citations

Soft Iterative Quantum Receivers Approaching the Helstrom Limit Using Realistic Quantum Devices

Chenjia Wei, Xiaolin Zhou, Lingda Wang +2 more

One of the most crucial challenges in quantum communication is the discrimination of the non-orthogonal coherent states approaching the Helstrom limit. In this paper, a soft iterative quantum receiver is derived for discriminating among the coherent states. The receivers employing the iterative strategy for optimizing the feedback measurement are capable of operating closer to the theoretical error probability limit, actuating about 1.05 dB improvement over a recent proposed quantum receiver. The iterative quantum receivers achieve excellent performance despite using a reduced number of feedback measurement steps. Monte Carlo simulations are performed for quantifying the influence of practical quantum-domain impairments. These results suggest that iterative detection offers substantial robustness against many imperfections degrading realistic experimental implementation.

IEEE Access•Jan 1, 2018•7 citations
We demonstrate an optical receiver that achieves the quantum Chernoff bound for discriminating coherent states from thermal states in the multicopy scenario. In contrast, we find that repeated use of the receiver approaching the Helstrom bound for single-copy measurement is suboptimal in this multicopy case. Furthermore, for a large class of multicopy discrimination tasks between a pure and a mixed state, we prove that any Helstrom-bound achieving single-copy receiver is suboptimal by a factor of at least 2 in error-probability exponent compared to the multicopy quantum Chernoff bound. This behavior has a classical analog in the performance gap between soft-decision and hard-decision receivers for detecting a multicopy signal embedded in white Gaussian noise.
We derive the quantum limit on the error probability exponent for discriminating any MMM multimode coherent states of light and show that it is four times that of an ideal heterodyne receiver for the same signal set. We then propose a receiver that achieves the quantum limit using auxiliary coherent-state fields, beam splitters, and single-photon detectors. The performance of the receiver is compared to standard measurements for various imaging and communication tasks. A related receiver for discriminating arbitrary multicopy pure quantum states is shown to achieve the MMM-ary quantum Chernoff exponent and does so using only local operations and classical communication.
One of the fundamental tenets of quantum mechanics is that nonorthogonal states cannot be distinguished perfectly. When distinguishing multiple copies of a mixed quantum state, a collective measurement, which generates entanglement between the different copies of the unknown state, can achieve a lower error probability than nonentangling measurements. The error probability that can be attained using a collective measurement on a finite number of copies of the unknown state is given by the Helstrom bound. In the limit where we can perform a collective measurement on asymptotically many copies of the quantum state, the quantum Chernoff bound gives the attainable error probability. It is natural to ask, then, what strategies can be employed to reach these two bounds---is entanglement across all available modes always necessary or can other, experimentally more simple measurements saturate these bounds? In this work we address this question. We find analytic expressions for the Helstrom bound for arbitrarily many copies of the unknown state in simple qubit examples. Using these analytic expressions, we investigate whether the quantum Chernoff bound can be saturated by repeatedly implementing the MMM-copy Helstrom measurement. We also investigate the necessary conditions to saturate the MMM-copy Helstrom bound. It is known that a collective measurement on all MMM copies of the unknown state is always sufficient to saturate the MMM-copy Helstrom bound. However, general conditions for when such a measurement is necessary to saturate the Helstrom bound remain unknown. We investigate specific measurement strategies which involve entangling operations on fewer than all MMM copies of the unknown state. For many regimes we find that a collective measurement on all MMM copies of the unknown state is necessary to saturate the MMM-copy Helstrom bound.
Discriminating coherent states of light is an important instance of quantum state discrimination that is central to all applications of laser light. We obtain the ultimate quantum limit on the error probability exponent for discriminating among any M multimode coherent-state signals via the recently developed theory of the quantum Chernoff exponent in M-ary multi-copy state discrimination. A receiver called the Sequential Waveform Nulling (SWN) receiver is proposed for discriminating an arbitrary coherent-state ensemble using only auxiliary coherent-state fields, beam splitters, and non-number-resolving single photon detectors. An explicit error probability analysis of the SWN receiver is used to show that it achieves the quantum limit on the error probability exponent, which is shown to be a factor of four greater than the error probability exponent of an ideal heterodyne-detection receiver on the same ensemble. Apart from being of fundamental interest, these results are relevant to communication, sensing, imaging, and quantum information processing systems that use laser light.
Understanding the fundamental sensitivity limit of an optical sensor requires a full quantum mechanical description of the sensing task. In this work, we calculate the fundamental (quantum) limit for discriminating between pure laser light and thermal noise in a photon-starved regime. The Helstrom bound for discrimination error probability for single mode measurement is computed along with error probability bounds for direct detection, coherent homodyne detection and the Kennedy receiver. A generalized Kennedy (GK) receiver is shown to closely approach the Helstrom limit. We present an experimental demonstration of this sensing task and demonstrate a 15.4 dB improvement in discrimination sensitivity over direct detection using a GK receiver and an improvement of 19.4% in error probability over coherent detection.
We consider the problem of detecting the true quantum state among r possible ones, based on measurements performed on n of copies of a finite dimensional quantum system. It is known that the exponent for the rate of decrease of the averaged error probability cannot exceed the multiple quantum Chernoff bound (MQCB) defined as the worst case (smallest) quantum Chernoff distance between any possible pair of the r states. This error exponent is attainable for r pure states, but for the general case of mixed states only attainability up to a factor 1/3 is known. Here we show that the MQCB is attainable for mixed states if there is a pair which is closer in quantum Chernoff distance than 1/6 times the distance between all other pairs.
One of the most crucial challenges in quantum communication is the discrimination of the non-orthogonal coherent states approaching the Helstrom limit. In this paper, a soft iterative quantum receiver is derived for discriminating among the coherent states. The receivers employing the iterative strategy for optimizing the feedback measurement are capable of operating closer to the theoretical error probability limit, actuating about 1.05 dB improvement over a recent proposed quantum receiver. The iterative quantum receivers achieve excellent performance despite using a reduced number of feedback measurement steps. Monte Carlo simulations are performed for quantifying the influence of practical quantum-domain impairments. These results suggest that iterative detection offers substantial robustness against many imperfections degrading realistic experimental implementation.